Touring - componet upgrades

Time to upgrade. I have stock componets on trek 4300(Suntour crankset,sis shimano front der and acero rear der.) I want to do more touring with this bike. I was thinking along the lines of xt crankset, xt rear der, lx cassette and chain. I def have to get new chain and cassette. They are slipping. Should I spend the money on front der and crank or would I be fine with whats on it already?

Just out of curiosity, what is a 4300? Is that a road, touring, or hybrid? How old is it?

I work on and tune up a bike for a friend of mine who doesn't tour but rides alot on the bike path. His '95 Schwinn Searcher Transit has Tourney deraillers and low-end Grip Shift and they're doing fine after 10,000 miles. I always suggest (this is just my opinion) that if you're going to upgrade you should do the most important parts, like the hubs (especially the rear hub), headset and bottom bracket. Anything else is just to impress your riding buddies.

Edit: The Acera rear derailler on my son's Kona failed after about a month but I think that was defective to start with, so there's always the exception!

My Acera rear derailer is badly corroded after just three months of riding.
Getting an XT to replace it.

smurfy, what bike path does your friend ride? The miami path? I am interested in coming down to ride it. Any info on it from you would be appreciated.