Journey is a *must play* game, that's a given. I guess the only question is: if you have both a PS3 and PS4 and have yet to play Journey, should you wait for the PS4 version? I don't see how the PS4 version could be worse and it certainly will provide an influx of players which is a plus for the critical online component of the game. That being said, the PS3 version is available right now, is probably cheaper than what the PS4 version will be, even a low number of concurrent users is enough for the game and when I played it I certainly did not feel like the PS3 was struggling to run it in all its glory (it's more about art direction than poly count).
Unfinished Swan was also a very neat little game that I would recommend to anyone and everyone. I don't see how a PS4 version would be much of a boost for that game, so I would lean clearly toward buying it now on PS3 if you have the opportunity.