its just not that big of a deal.
I have 10 vc games and every channel and I still have half of my memory available. I have played a ton of games that i have bought and rented. I still have all of their save files.
Worst case scenario, if you buy a ton of vc games or wiiware games you can buy a cheap 2G SD card or delete something and re-download it later if you decide to use it again.