Somehow I doubt that the heads show absolutely no sign of wear if they're actually 10 years old and have been played regularly. I'm guessing they're clear since coated heads would most assuredly have uncoated spots. Even in a clear head playing over a period of time will scratch the head and create a satin finish rather than the clear it started out as.
As far as changing them I would say it's always a good idea to change them regularly. I don't think there's any value in playing with excessively old heads for any sort of tone benefit since most any head can be tuned to any tone you could desire. Heads are made of plastic, and plastic deforms. Go grab any plastic item you want and bend it. You'll see stress marks from bending.
The head is constantly under tension on a relatively sharp bearing edge, being hit with a very small diameter stick at high speed. This force alone puts stress on the material and causes deformation, which over time cannot be corrected by its elasticity. This causes the head to become stiffer, or asymmetrical in stiffness, stifling vibrations. The area that sits over the bearing edge gets the worst of it, as the only thing keeping it straight is the hoop. One of the most important things when it comes to heads is keeping the entire diameter of the head in contact with the bearing edge, which becomes hard to impossible as the head warps from use. Tuning drums is hard enough, but when the head is uneven getting even tuning from all the lugs makes it harder.
The steel hoops that keep the heads on may also be deformed and years of dirt and debris are certainly trapped inside. The bearing edges themselves may be damaged, or lugs or lugs screws may be bent. If you haven't taken it apart recently to check these it's definitely time.
So yes, I would say new heads would make it sound better.