You probably won't see much, I think VCXOs are usually in the +/-1kHz tunable range. You'd see a few lower digits change as you vary the control voltage, and not much else (plus probably not having a reference to calibrate it against).
Maybe more interesting to look over the circuit itself, see what chips they used, what the logic diagram is? Dunno. As you say, it's only $25, so do with it what you like!
Other ideas might be, improved front end comparator / level control / prescaler for higher frequencies, etc.? Not much use if you don't have a scope to prove operation, or faster signal generators / scope to see that it's working.
Bonus points would be getting the count correct while using a prescaler. That might be tough without ripping out all the logic, though.
Tim