i have a copy waiting for me since monday that i haven't installed yet, only 9.99 w/ a new mac. it was a no brainer for me --- but if yours isn't new you can do what a lot of ppl i know are doing. find 4 ppl that want it (or convince 4 ppl they need it) and split a family pack which includes 5 serials for 50 bucks.
i think all the internal upgrades are definitely worth it, from what i've read anyway.