I use a Nikon 4000 (35mm) for slides and negatives. I also have a need to scan 4x5 transparencies. I've tried an Epson 3200 Photo and, while I was happy with the reflective scanning, I found the scans of transparencies to be a bit too fuzzy.
In the past year I've gone to Windows 7 and needed to upgrade the Epson to a V750M (no drivers for the 3200). The reflective scanning is improved over the 3200. I have not tried scanning transparencies but I will note that the 750 has an oil-mount kit which should improve the clarity of the scans. That said, I have not tried the oil mount as yet. You can see Aztek's claim to resolution improvements at http://www.aztek.com/Epson%20V75...
A film scanner will bump-up your scan quality at a price. As you likely noticed, high-end scanners like Flextight are very expensive. Also, cost increases dramatically with the transparency size.
You might consider looking for a used Nikon 8000/9000 scanner. With the move to digital workflows some of these are making their way to the used market. It may be a way for you to bump-up the quality without as big of a drain on your wallet.
I will also note that software will improve your scans. I recommend Silverfast http://www.silverfast.com/
and have used their software for many years. The software supports IR dust removal so long as your scanner supports IR.