Ditto on most of the above. Profiling my scanner (Nikon Coolscan V) with one of the Lasersoft targets did help get me more accurate color. It still needs a bit of adjustments to match what I see in the slide, but it's much easier to get there after profiling. This is probably because I'm playing a bit fast and loose with my scanning/profiling. I tried Vuescan's profiling solution (very easy to use) but ended up liking the profile I built with ArgyllCMS more.
I scanned (single exposure) the target slide with Vuescan and saved a raw linear scan. I built a profile with the resulting file. For the profile to be valid, you are supposed to use the exact same exposure settings for all of your scans. Instead of doing that (me playing fast and loose as mentioned above), I let the scanner figure out exposure. I also use the multi-exposure option, where Vuescan does a high and a low exposure to get more out of the shadows. Save as a linear scan. I then bring it into Photoshop and assign the profile that I built with ArgyllCMS. Convert to AdobeRGB and tweak. The 'tweaking' in this case usually involves a curves adjustment layer to bring the black point of the blue curve up a little bit and moving the midpoint of the RGB curve up to lighten everything up a bit. This is saved as an action so I can run it automatically and optionally tweak my default adjustments.
It might all sound a bit complicated, but once the profile was built, I can do rough color corrections on Kodachrome slides pretty quickly - less than a minute per slide? Of course, finer adjustments and dust removal takes longer... For the finer adjustments, I pull the slide out and compare to what I have on the light table.