Well it really depends on whether or not you are interested in unlocking the regis in platinum. Since the regigigas event ends on saturday. If you already have Ruby, Sapphire, or Emerald, then you might not be too worried about unlocking them in Platinum.
Personally, I'm only getting the event for 2 reasons. 1 because it is an event pokemon. 2 because I want to be able to play platinum for as long as possible, so the more stuff I have to unlock, the longer I'll have something to kill time.
I'm typically inactive between Spring and Fall. I'll be on as often as time allows.