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Since you have he Vuescan software and the Nikon rig is still running, my recommendation would be to keep using it till it dies.
I have a plustek 7600, still running the old silverfast 6.6 software. Yes, it scans at a higher dpi, but the biggest improvement is actually the software......essentially you are able to do a lot of "up front" adjustment on your slide/film at the scanning point, and do multi-pass scanning to increase image depth and decrease noise levels (as long as you are not in a hurry or don't have a lot of slides to scan). I really like the rig and am considering the new silverfast software upgrade (8.x), but honestly, if my old HP scanner was still working, I would still be using it, thus my recommendation to you.