I really think dragons need to be unlimited. What is to be done after you've killed all of them?
No. If dragons are infinite or in too great abundance, much like the gates of Oblivion, they will suffer the same fate of repetition, boredom, and ultimately an uninteresting feature.
Dragons need to be powerful. Dragons need to be vicious. Dragons need to make the hairs on your neck stand up when they roar. Dragons also need to be LIMITED. There is only one Dragonborn. The rest of Skyrim is more than likely screwed when it comes to combating dragons. It makes more sense for them to be powerful, yet rare as to not make them seem common and uninteresting.