I have recently taken up woodworking and I am thinking about buying a
jointer (6" floor model). My question is how useful/essential do you
think a jointer is for a hobbyist? I already have a table saw, router,
drill press, hand tools, and most of the basics.

However, I really only have time for a few projects a year... things
like bookcases, chests, shelves, side tables, etc. All of the wood I
buy is surfaced on four sides (i.e. I don't have the time to buy rough
cut wood and clean it up, plane it down, etc). Is a jointer really
worth the investment in this case?