When will SSD drives catch up in storage capacity and price to traditional spinning platters?
Never. Someone did calculate that if you can get flash that lasts 15 years it would be cheaper than disk, though (because the disk has to be replaced). I can't find the links on those.
Also what about the life cycle of drives that get powered on and off repeatedly?
We wrote a paper on that topic where we treated start-stop cycles as a resource to be rationed with a token bucket filter: http://storage-conference.org/2011/Papers/Research/10.Felter...