I just buy whatever and whenever
I'm sure pretty much all of us have a mix of old and current generation machines...... And to be honest all the current gen consoles will not make good collectors items in the future as they are not exactly what i would call "reliable"
I think the oldies from Sega could survive a nuclear fallout
I will never buy a new console on it's launch date ever again!! I will wait a while so all the bugs can be ironed out in later hardware revisions.... and it will be cheaper