hmmmm....
Resource - Edit Calendar is available OOTB as an instance permission. I'm 90% one could make a process like the Set PM as Collaboration Manager process that automagically grants each resource edit permissions on their Calendar...
I see all kinds of opportunities for these little 'helpers' here but not enough time to do 'em all. If someone else wants to jump on this - go for it. Otherwise, maybe I'll stick my nose into this if its quiet over the December holidays.