Are there any plans for a Mercury Rev live album?

There seems to be a good chance of it.
In an August '99 chat, Grasshopper said, "We may release some live recordings at some point. We tape every show."
And in 2002, James Shaw, the band's sound engineer said, "I wouldn't hold your breath, but somewhere over the rainbow... Every show is not necessarily "professionally recorded", though all the shows are recorded with some rare exceptions due to technical reasons. I record all the shows from the sound desk with some microphones on the audience mixed in, but these recordings are rarely good enough for a "pro" live album. Though some of these recordings have showed up on the web site and on the B-Sides of the Dark Is Rising UK and EU singles/DVD. Once in a blue moon the show is multi-tracked, and a collection of these is slowly building, to see the light of day."

How about another rarities album?

Yeah, maybe. Here's an except from an interview with Grasshopper..
"This record (Deserters) is also a lot different in that we've learned a lot of production and miking and stuff. That got to be pretty easy with guitars and that, but when we started using saws and all the violins, it gets a lot tougher to get it on tape and have everything in its space. That took a while - it was a lot of trial and error, and sometimes it didn't work. We had to throw out a bunch of stuff, some instrumentals we tried." Some of the material may see release as future b-sides, and Grasshopper hopes to see a Lego My Ego Vol. 2 including some of this material as well as other unreleased projects recorded since the release of the first volume.

Update: A 2-disc collection called The Essential Mercury Rev : Stillness Breathes 1991-2006 includes a second disc containing various rare tracks, most of which previously available as b-sides or on compilations.

Does the band allow taping of their live shows?

Scott Judd says, "rev's concert soundman told me in person several months ago that they encourage taping of shows, and he has since proven that by getting me past security at least once to do so, though he has also qualified that by allowing microphone-only recording, NO soundboard feeds."

What's the Tettix Wave Accumulator?

The band uses this piece of equipment from time to time, such as in the hidden track at the end of Deserter's Songs and on the track "A Kiss From An Old Flame" on SYOTOS.
Grasshopper says, "A tettix wave is a musical machine that jonathan and I invented with U.S. patent pending..."
Someone on the rev mailing list adds,"The Tettix wave accumulator takes up most of the room in Grasshoppers basement. A smaller version has been used on the road. I believe both Jonathan and he built it. I do not know whose idea it was originally."
I found another article, in which Grasshopper says, "The Tettrix was an idea I had to get a bunch of oscillators and, instead of controlling them through a synthesizer, I worked it so that you could plug anything into it and also store it on disc."

What's up with that red, white, and blue curved star that Mercury Rev seem to sometimes use as their logo?

It's actually the American Revolution Bicentennial symbol. The Rev have used it as far back as their first single (Car Wash Hair).

What's up with the line in "Frittering" about a glacier making its way down to the _____?

The thinking was, it was probably rind. Rind is a an ice that forms on top of mountains that are in the cloud deck. The moisture from the clouds forms a thick ice that will gradually accumulate and if it stays cold enough, long enough a glacier will form. If you chip away the glacier you will only have dirty old rind ice.
Chemmie sets it straight, "the glacier makes it's way down to the Rhine. This is official - from the typing fingers of Dave Fridmann, no less. It's 'slow as a glacier' and 'bottom of yer room' (which sort of rhymes with soon)."
The Rhine is a big river in Germany.
But Jonathan was likely referring to the Rhinecliff hotel, a place in upstate New York where the Rev and Harmony Rockets used to play often. Adam Snyder has recently played some solo shows there, by the way.
 

Why don't they ever play songs from Boces live anymore?

Since touring for the album in 1993 and asking David Baker to leave the band, they've rarely performed Boces songs live, with the possible exception of "Boys Peel Out", which didn't completely fall off setlists till the All Is Dream tour. Also, "Downs Are Feminine Balloons" was performed at least once since, in Los Angeles in April 1999.
In a 1996 interview, Jonathan explained his apparent aversion towards the album: "Boces was really painful to make. There was a lot of drug abuse and alcoholism, just a lot of tough times making it. I love it a lot, but it’s kind of like seeing an ex-girlfriend where you had a really painful breakup, and it’s just not easy going up to her every night and saying, ‘Hey, how’s it going, how’s your new boyfriend.’ It’s one of those situations, so every once in a while we’ll choose something off there, but we really gotta work up to it."

Who is Paul Sharits? (regarding the obscure Rev b-side "The Left-handed Raygun of Paul Sharits")

I don't really know much about him, but I believe he was an avant-garde New York film-maker in the 70's. Vega Rd adds: "One of Paul Sharits' films is called Ray Gun Virus. and he used to teach at the University of Buffalo where Grasshopper and David Baker studied something to do with films (didn't they?). but i dunno if they were students of his, i think he worked there before their time. sharits died in 1993."

Who is Robert Creeley? (regarding the Rev b-sides "So There" and "I Drempt")

Robert Creeley was a prolific, influential poet who went on to become a professor of poetry at SUNY Buffalo. Says Jonathan: "I took a lot of English classes with him, he’s a great poet and a big influence. I can’t remember if I ever even graduated…I don’t think I did, because I went out on tour and stuff like that. Creeley grew to become our—what’s the word?—mentor or something. We studied and we talked with him a lot just about different things, we were really in love with what he was doing and still are."
Creeley died in March 2005 at the age of 78.
For more info: http://en.wikipedia.org/wiki/Robert_Creeley

How many Peel Sessions have the Rev done?

five.

first one (recorded 27/8/91; broadcast 5/10/91):
chasing a bee (chasing a girl [inside a car])
syringe mouth
coney island cyclone
frittering
--
second one (broadcast 14/8/93; rptd 17/12/93)
trickle down
boys peel out
downs are feminine balloons
--
third one (broadcast 29/7/95)
everlasting arm
i only have eyes for you
racing the tide
close encounters of the third grade
--
fourth one (rec. May 5, 99; b'cast May 25, 99)
i don't wanna be a soldier
the funny bird
tonite it shows
observatory crest
--
fifth one (rec. Oct 11, 01; b'cast. Nov 15 01)
Tides Of The Moon
Little Rhymes
Spiders & Flies
Planet Caravan
Gymnopedie 3
Hercules

These were all compiled and released on cd in 2009 on Mercury Rev - The Complete Peel Sessions.

What songs have Mercury Rev covered over the years?

Here is an almost/kinda complete list:

How about songs they just covered a little bit of (but not close to the entire song)?

Who have Mercury Rev opened for over the years?

here are a few..(in somewhat chronological order)

Bob Dylan (one show: Yale University, 1991)
Flaming Lips
Porno For Pyros
Ride
Spiritualized
Dinosaur Jr
My Bloody Valentine
Hum
Jesus and Mary Chain
Bob Mould
Buffalo Tom
Sparklehorse
REM
Oasis
Doves