Sell the 21.5 inch for about $60 and buy a 25inch crt with svideo for about $25, then with whatever money you have leftover take the wife out for dinner. Problem solved.
If your putting anything in a midway cab, nothing looks as good as a 25" crt. Its was a easy choice for me and it looks almost OEM. The resolution in the long run will be better then if you put a LCD in there. 99% of mame games are older and look to pixeled on a lcd, they need that slight image blur to make them look nice. I thought about throwing a 26" lcd in my KI cab, and I just couldnt get past the crisp flat picture for all the old games, The lines were to sharp and there was too much motion blur caused by the lcd that it actually made it look worse! Trust me on this one, CRT is the way to go and if you look, you can find a 25" tv with svideo for like $25 on CL or Ebay or at local garage sales, flea markets, etc!
Good Luck.