One important aspect to remember is that a lot of high-end upgrades are for no other reason than to shed grams. Being the Clyde thread, i believe we all know where the eaisest place to shed real weight is, and it aint the seatpost.
I would look into upgrading components up to a certain level, but only as they break down. Also, depending on how much you paid for the bike, and how old it is, I would think about creating a bike fund. Save a certain amount of money every month until you can upgrade to a better all-around bike. Only put money into your current bike to repair problems.
Most upgraded modern equipment is for 9 speed rears on MTBs, so if you have a 6 or 7 speed, you may not have a lot of upgrade potential anyways.
If anyone disagrees with what I've said, please feel free to correct me, I am in no way trying to sound like an authority on the subject, this is just my opinion.