Would be glad to see a return to the 24 month cycle rather than this crazy 12 (or even 6 month in some cases) cycle we presently have. Of course, naturally no-one is asking me to upgrade every x amounts of months, I'm doing it out of my own choice (and probably vanity).
In the Samsung world, I don't really see any need to change from an S3 to an S4, let alone to an S5. If, however you are on an S2, may be time to move up to an S5.