Modern high-end LCDs are fine for gaming. They have greatly improved black levels and overall contrast in the past couple years, especially with LED backlighting. Low end TVs are still kinda blah, but the high end Samsung and Sharp stuff is amazing. I actually mistook a Samsung LCD for a plasma about a year back when walking along the "wall of TVs" at Best Buy, and I have a pretty sharp eye for that sort of thing. Just remember that you can't cheap out. If you want a good 32-37", expect to drop at LEAST $1000, and probably more like $1800 or even up to $2200. While there are sets in this size range for ~$500-600, they simply don't have the performance you need for this application.
You'll probably need to set things "properly" to get a good picture. The correct setting on LCDs for brightness is generally ~20%, contrast ~90%, and backlight ~80%, though this of course varies with brand, individual TV, and applied signal. Most TVs will ship with all three controls cranked to or near 100%, which results in a grayish, washed out picture. CRTs are often like this, too, but the result isn't quite as objectionable to most. Yes, when you set it right, it won't appear as "bright" as before, but it'll look a lot better. Also, if there is a sharpness control, usually best to set it to 0.
Just watch out for scaler lag. Do the "lag check". This involves bringing in a laptop with TV and RGB (and preferably DVI) out to the store and displaying timecodes. You then take a picture with short exposure time of both displays and compare the timecodes. Use an old-fashoned analog TV and CRT PC monitor to get a baseline in case your onboard screen or TV out lags (they generally shouldn't, but who knows). On interlaced signals (so svideo/composite out, mostly), a half frame (field) is fine and almost unavoidable on progressive displays like LCD and most plasma, but anything more than a full frame makes it pretty much unsuitable for gaming. Make sure to test all inputs in all resolutions as scaler lag can certainly vary.
As far as using MAME with a widescreen, you'll have to set a "barn door" (black bars on the sides) option to have just about anything display at the correct aspect ratio. Vertical games will be really bad in this respect and only use maybe 1/3 of the screen. If you are one of those crazy people who doesn't mind stretched graphics, then you could stretch it to full screen, but you'd never see me do that (or tolerate it). The graphics won't look "authentic" down to the scanlines you may be used to on older games, but medium res and VGA games should look awesome.
Like qrz said, don't expect to service a LCD or Plasma TV beyond maybe capping the power supplies if they should go bad. There simply aren't many servicable parts, especially if you can't swap SMT parts. Should it break out of warranty, you'll be trashing it and buying another. Given that yours won't see nearly the usage an on-route game would, this isn't likely to be an isue.