Three years old and lots of dusty trail riding, but how many miles? Is this the first time you have serviced your hubs? I'd replace the bearings, repack with grease (I prefer a silicone based synthetic but any decent grease will do), and make sure you tighten them just to the point of getting rid of play. When you reinstall, check how true the wheels are and make sure the brakes are adjusted so that you don't have any drag. As mentioned, proper tire inflation is also important to prevent that riding through mud feeling.
If you haven't checked you bike fit in three years, you might want to do so. As your fitness improves you may find that you need to tweek positioning from time to time. Adjustments also have a way of migrating a bit over time if things aren't periodically checked and tightened. Even seemingly minor adjustments can make a significant difference in comfort and pedaling efficiency.
Take the chain off, or have your LBS do it and use a caliper or chain gauge to determine how worn it is. Replace if it is at or near the end of its expected life, which is determined by wear, not age. While the chain is off, clean and inspect your rear cassette and chainrings looking for any damage or wear. With the chain still off, slowly spin the cranks holding on to each pedal one at a time. Feel for any drag or roughness in the pedal spindles or the bottom bracket. Then give the crank a good hard spin while holding onto the seat tube (make sure your hand is clear of the spinning cranks) to feel for excessive vibration or grinding. The crank should spin several revolutions freely when given a good hard spin. Check your crank arm bolts/nuts for tightness. Lean over the top tube of the bike putting some weight on it and grab the cranks. Feel for play with the chain off. Clean and lube the rear derailleur. Clean and lube or replace the chain and reinstall. Put the bike on a rack or suspend it from a rafter in the garage so that you can spin the drivetrain freely and adjust both derailleurs.
This whole process should take just an afternoon or so and should be completed about once a year along with a good general cleaning, inspection and lubrication of cables, pivots, shifters, brakes etc. I do my major maintenance in the fall on the two bikes I have that are stored during the winter. My winter bike (which is also my trail bike) gets serviced in the spring.
A Trek 7200 is never going to be a fast road bike, but these steps will keep it running smooth. Here are some links with more detailed info:
http://www.parktool.com/blog/repair-help
http://www.sheldonbrown.com/articles.html
I suggest that you perform a complete cleaning and maintenance on your bike before considering "upgrading".