While I have no experience with the Nikon you mention, I can speak as to the Imacon scanner and a few others. I presently own three scanners, and each has its own uses.
The king of my collection is a Howtek Scanmaster D4500, which although considered bottom of the barrel for drum scanners, really does put the CCD scanners I own to shame. For scanning underexposed Kodachromes, it's the only one that will dig out any shadow detail. However, the quality it gives comes at a huge price in terms of convenience, since you have to mount the film to a drum using oils and clear acetate. I can certainly praise Silverfast as a really nice scanning software. Without it, my Howtek would be pretty much useless, since the software that came with the scanner was terrible. Silverfast makes the scanning part pretty easy. And yes, the Howtek does a fine job with negatives as well, but it is so inconvenient to use, I greatly prefer my Imacon for negatives.
I have the low end Imacon 343, which I bought exclusively for scanning 6x7 negatives. It works really well for that task, since any problems the CCD might have with density in the film end up in the highlights, not the shadows. The Imacon is really easy to use, and their software is pretty nice, though I still think Silverfast is a bit nicer overall. I should mention that all my negatives are B&W, though I have scanned some color negatives, but was not happy with the color balance. The 343 is OK at 35mm chromes, but it really can't dig much detail out of the shadows. It's also a bit weak in the resolution department for 35mm, but it still makes nice scans if you don't care too much about extra-fine detail.
The oldest and least used scanner in my collection is a Polaroid Sprintscan 4000, which was all the rage many years ago. I still use it to scan 35mm slides if I'm in a big hurry and don't care much about the results. Once again, Silverfast really helps out, since it is far better than the Polaroid software. From what my friends tell me, the newer Nikon scanners are much nicer than this old Polaroid.
It's worth mentioning that I bought the Polaroid new, and the Imacon and Howtek used. Used scanners are worth next to nothing these days, so you can really get some deals if you look around. And I agree that when it comes to software, you do get what you pay for. Most of the free software that comes with scanners is pretty bad compared to Silverfast. I'm still using the old versions that I bought several years ago, and they work just fine.
You can't go wrong by surfing the web for opinions on scanners, as there are thousands of them out there, but like all opinions, they are best taken with a grain of salt. Since you want to scan negatives, pay particular attention to that, because in my opinion, negatives are much harder to scan than chromes. I'm just so happy that digital imaging finally came of age, so I could abandon film altogether. Scanning is a very laborious and time consuming process, that even when done right, still doesn't produce as nice of results as capturing a digital original.