I'm a big proponent of keeping everything hooked up. Why the hell not? Games are worthless if they're not accessible. Yes, you could hook up that dusty nes any time you want, but do you really want to? My setup, although admittedly on the cheap, is a good example of how to keep things uncomplicated...
I have a black 3.25' x 1.75' x 1.75' tv stand. Sound tiny, right? Well, my TV is currently hooked up for six different inputs. I can watch or play games from the computer, with great 2.1 sound and two ps controller, one cordless, and then I have a Dreamcast, Gamecube, N64, Genesis/32x/cd (with enough room for game+genie) and a teeny DVD player. Sadly, there's a couple black switches that keep the av in line, but $15 is way better than $100+ for a good tuner. I also managed to cram 109 genesis games, 26 32x games, 24 n64 games and 56 Gamecube game into the little black wonder.
It's also worth mentioning that due to Jacqui's and I's bundle of weaselly joy, I zip-tied all the cords the best I could and managed to squeeze the entertainment center as close to the wall as humanly possible. The little bugger was stashing food behind the sega cd... Now he just tried to paw at the glass door on the front now and again. I kinda miss watching him climb to the summit of the 32X though. Congratulations Weasel, without the aid of a sherpa, you have managed to conquer mount 16-bit excess...