No one really knows, because Apple has been changing the way they release software, so history doesn't serve well as a guide. In previous years, they've always done updates from 12-24 months apart, but we don't know what they'll do this time. There will almost certainly be an update to iPhoto at least within the next couple months, related to iCloud, but it'll almost definitely be a free point update, not a paid upgrade. They may never choose to release a paid upgrade again, with the App Store model, or they may continue with a similar schedule to what they had before, just with per-app pricing as they have now.
Incidentally, I'm hoping they update or replace iWeb, instead of trashing it altogether. Don't care much about iDVD, although I know people who would like an update, but I think that's unlikely with the cloud focus now.
jW