Define "enhance it". Do you mean just perform preventive maintenance by replacing those items that will eventually wear/fail or do you also mean to increase performance? Another wear item to consider is the water pump.
As far as your coolant leak, the 4.0L is known for chronic t-stat housing cracking as Stang-aholic mentioned above. The OE housing is made of plastic (duhhhh).
Also, it sounds like it's time for a clutch.
Here's a link to the repair manual: http://iihs.net/fsm/?dir=1