Unfortunately, PrE only offers so many Effects for such corrections and improvements. It sounds like you have tried most already.
When doing density and color corrections, I start with Levels, and then work on to the color Effects. PrE offers these with the Auto function, which I find often lead to a bit of "strobing" of the Effect.
I use PrPro much more, and for each of those Effects, there is a manual version too. It makes for more work, but allows much more control. That program also offers many more Effects for both density and color correction, such as RGB Curves, Fast Color Corrector and then the big-brother (but much more work) Three-way Color Corrector.
Above that, Adobe AfterEffects includes many more color and density Effects, plus also Cloning of areas, kind of like Photoshop, to working on those "spots." However, that program has a bit of a learning curve, though offers so very much power.
One side-note: having had the telecine work output to DVD has already compressed the footage to MPEG-2, so much data has been lost. If you edit, and then output to a finished DVD, you will be compressing that footage again, and quality will take a hit. It might not be enough to worry about, but will be there. Only you can tell if it is high enough on the quality scale to be usable. The ultimate telecine output is miniDV tape, which would then be Captured via a miniDV tape camera over FireWire, or from a miniDV tape deck over FireWire.
PS - one trick that might improve things would be to place a second Instance of your video onto the Track above. Reduce the Opacity of that second Instance to about 50%. Apply the Effects to both Instances of the Video. Might not give you enough correction, but I would try that as a test. Also, experiment with the Opacity of the second Instance, to see if you can get an improvement.