Depending on the item I purchase, I keep the box for 30 days if I think there's going to be a return involved in the short term with an absolute limit of 'when I can't remember when I got it, it gets tossed'. Granted, I've made some exceptions to this rule (PS3, iMac) where the boxes have been kept specifically to protect the item if it's in transit.

Realistically, the Wii is a long way off from ever being considered collectible - like, a couple of decades off. If you really want to get one for collecting purposes, go buy another one, keep it in the box, and put it somewhere you'll never touch it. Play the other one and wait for the other one to gain nostalgia factor.

I completely understand the hoarding aspect of it; the sheer amount of stuff I got rid of when I moved across the country was staggering. Even I didn't know I had that much stuff. And I still have my original Odyssey2 and Vectrex in their boxes - but again, they hit collectible status a few years back and even then the boxes were kept by accident.

I'm sticking with tossing the boxes and finding one to put aside. Bear in mind that a clean, unopened, unplayed unit will always be worth more in the future, too.