Thanks everyone for responding!
My PC is up to snuff - I play pretty much everything maxed out at 1920x1200 ...
Modded 360s can play "back ups" of xbox games, which is the only reason I would want a modded one.
My main use would be for two player split-screen when a friend comes over--coop fps and fighting games, mostly. I don't really care about Live as I have a pretty poor internet connection and won't be paying for any Live subscriptions. I did originally want to get a 360 because I felt I was missing out with Gears of War, but now that is coming to the PC ... Still there are some exclusives like Dead Rising or whatever that zombie game was called that I'd like to play, and I'm sure there will be more down the line ...
Yeah, it's called Dead Rising (and it's awesome)
Although, I discourage going for a 360 if you're not going to use Live. Why? Because half of the 360 is Live. And once you have it, you don't want to go back.
Just for reference, no one refers to them as "Modded" 360's, but rather "Flashed" ones.