Sully
I started with a Nikon LS-20, which is 2700dpi and has no ICE, these are SCSI only and IF you can get one in good condition then perhaps.
But to be totally frank I just don't use it anymore because I can get better results with the Epson 4870 than the Coolscan LS-20
now, lets make some assumptions here: Lets assume that the Nikon is 100% 2700 samples per inch scanning and that the Epson is only a 2000 spi real world scanner (I think this is a reasonable assumption, scanning at 2400dpi setting and down sampling to 2000 look quite clean).
will moving from 2000 samples per inch to 2700 make a real significant difference ... it is in fact only about a 30% increase.
you need to double the figure (4000 samples per inch) to make a significant difference at capturing more details.
It remains to be seen if the scanners like the Plustec which claim 7200dpi actually do more than subdividing a blurry image into more pixels of the same blur.
Optics play an enormous role here (its not just numbers) and a crappy lens will make higher resolutions impossible. Try using a $50 x200 microscope vs a high quality Olympus or Zeiss one in a lab ... there is a reason they cost thousands.
Good flatbed scanners have good optics ... it makes a huge difference
The next problem you'll face is age. Things are getting dirtier inside with foggy buildup on mirror surfaces, this will degrade your image. Go read this guys site:
http://www.sebsgarage.com/2005/11/cleaning-nikon-coolscan-iv-ed-ls-40-film-scanner
check out the buildup he found on the mirrors
I live in Finland, we have double glass inside windows with a third pane on the outside. No matter what after 15 years the insides of the double pane set are foggy ...
even though they are sealed.
This means that any older scanner you buy will need cleaning internally. Fog makes a huge difference to contrast if nothing else.
I have owned
Nikon LS-20
Nikon LS-40
Nikon LS-4000
Epson 3200
Epson 4870
Epson 4990
I can say that for 90% of what I do with 35mm I use my Epson. If I'm after a big print of a specific neg then I pull out my LS-4000, but otherwise the 4870 will get as much detail as I get from the LS-40 (which is rated at 2900dpi, a smidge over the 2700dpi of the LS-20). I don't even use the LS-20 anymore as my Epson betters it in every way (especially scanning multiple strips of film in unattended operation... I don't particularly enjoy sitting there for hours watching it all happen)
What I really notice with the Nikons is you really really need to nail focus. You see as the optics get more precise, so too does the requirement of focus accuracy.
I recommend you read this page of mine
http://cjeastwd.blogspot.com/2009/03/nikon-iv-ed-vs-epson-flatbed.html
I think that unless you go and spend money on a scanner like the Imacon/Hassleblad V-5 then you will only be tinkering around the edges.
I expect that there is much you can do with learning to use your 4870 to better effect. I believe that its as good a tool as you'll get for the money.
Don't dismiss 'sharpening' as fudgery ... software fixes for your images can add a lot of value ... NASA seemed to have thought so when they applied processing to the hubble before they could get up to fix the optics[
1].
The error was well characterized and stable, enabling astronomers to optimize the results obtained using sophisticated image processing techniques
I've made prints from 35mm film to 40cm wide scanned with my 4870 ... noone has said anything more than they are great photographs. At 8x15 in size or even WWW sizes I'm sure you'll need careful analysis to tell the difference.
so, no in the < $250 area I think you'll be on a wild goose chase to improve over your Epson (unless its filthy an needs a clean)