What you say Ian makes some sense. With something like Kirby's Dream Land 3, the VC download doesn't cost very much compared to the original cartridge. It's also a way to try the game out to see if it's actually worth owning the original.
Though I'm not really a collector, I still have collectorial tendencies that I can't break. I simply cannot bring myself to play a downloaded game, not even ROMs which are free (don't care about the legality of them). It has to be the original format, on the original system, with the original controller it was designed for, otherwise it just doesn't feel right. I also like to display my gaming stuff on shelves and such, and you can't really do that with a download. Lastly, downloaded games can't be brought to a friend's place without lugging over the entire system; I have a similar problem with games which have save files that can't be copied to an SD card.
Anyways, I guess what I'm saying is that the VC is great for the average gamer, but is of no value to the collector. Fortunately we're a rare breed.