Cycling Gear: How to upgrade?

While being fairly new to riding, I recently purchsed a Diamondback MT bike, which I like so far. However in hindsight I am questioning my choice between that and more of a road bike. Is there much I can do to satisfy my curiosity with the bike I have, or am I SOL?

When I first started riding 2 years ago my first purchase was a Giant Yukon (I didn't know if I wanted to get a road or MTN Bike at the time)  My decision was made up because of the fear of riding on a road and that I used to race BMX on a very tricked out GT Box series in the ABA circuit.  I figured to closest thing to a BMX bike was a MTN bike.  I have to say that I enjoyed riding my MTN bike in Northwest Florida, lots of single track.  I only rode maybe once a week on the weekends though because I had to load my bike onto my car and drive to where I was going to ride (very difficult to do after a long day of work 12+ hours).  After a while I got bored with the fact that I wasnt getting much of a workout.  After moving to Texas I was very indecisive if I wanted to stick with a MTN bike or maybe make the switch to a cyclocross bike (much like a road bike, built like an SUV for offroad riding) after reading a lot of reviews from other riders I was sold on a cyclocross bike.  They are very durable offroad if the most your are gonna be doing is off road trail riding (i'm not sure how well they stack up for stump jumping and downhill).  Although I would suggust a Cyclocross when I finally did buy a second bike I went with a road bike for the fact that after a lot of thought I decided I would probably spend more time on the road in the future after having enough spiders in my path offroad it just kinda got tiresome and annoying.  My first road bike purchase was just an entry level cannondale synapse 7 and that was going to be it for me, until I got addicted to road bike.  Now I have a Jamis Eclipse that was a $2500, well spent as looking back at what I now prefer it is def road bike.  Just my opinion though.  If you really arent sure a great place to start is a cyclocross bike where you get the best of both worlds until you figure out what you want to do and then you can stick with the MTB and have the cyclocross as your winter/commute/trainer or go with the Roadie and still use your cyclocross as the winter/commute/trainer/bike for when your road bike is in the shop getting routine maitenance.