I think the value will go up. Most people don't take care of their stuff so there should be less of the games around in excellent condition. I've got plenty of CD's and DVD's going on close to 20 years now. They all play perfect.
Besides, PS2 games work right outta the package. These current games need updates, DLC transfers and none of the online playability will survive. I don't think this generation of games will be all that collectible, but the old school stuff should continue to be hunted.
Wouldn't you just need a machine that already has said updates? Seems like that would be a really easy DIY if necessary. There's no reason why that data will escape into oblivion just because the games are old. Besides, not a single update to any 360 game has required Internet connection for me, the "update" came on the disc. Only this latest gen has ever "required" Internet to update just so that it can play games after setup.
Was kinda thinking Xbox One or PS4 as this generation and not PS3 or 360. I'm sure the 360/PS3 will have some kind of price increase over the years (especially the one player games), but not as dramatic. No, the data doesn't just "escape into oblivion", but somebody buying the game 15-20 years from now most likely won't have the updates or patches on their hard drive for that particular game.