Ray, I'm doing an extensive amount of work on this issue, because I have a large legacy of colour negatives that I am converting to inkjet prints using the Minolta DSE 5400 - first model. I've been through everything you describe, and in fact I'm in the process of developing a write-up on a workflow that addresses colour negatives. The issues wouldn't be that dissimilar for positives, except that positives are much easier to colour balance, because there are IT8 targets for profiling positive films that don't exist for negative films.
My write-up will take some time to complete, because as your own experience indicates it is a bit involved. However, there is light at the end of the tunnel - I have produced A3 output that I truly think passes muster, and I shall soon be submitting for "peer review" to get a valued independent opinion. To anticipate some of my content, here are a few observations:
(1) There is no question in my mind that Silverfast Ai Studio is the best software option of the three you mention. If you will be doing a fair amount of this work, the outlay is worthwhile. It comes closest to giving you believable scans and has the most control points for achieving that objective. Better than Minolta DiMage Scan and VueScan by several country miles.
(2) That much said, it is quirky, with voluminous but poor quality documentation, which puts quite an onus on the user to figure it out. Their tech support people I must say are responsive where they can be. Taz Tally's Silverfast book provides value-added on the Silverfast manual, but it too leaves things to be desired. All said and done the learning curve is worthwhile if you will be doing alot of film scanning. The absolute first thing to beware of with Silverfast is that there must be ZERO blank space between the film and the film carrier for the image you are scanning, and the scan cropping frame MUST ABSOLUTELY fit within the actual image, otherwise you get garbage.
(3) Don't use the scanning software to get more than a roughly believable scan to start working with in Photoshop. None of the three software options holds a candle to Photoshop, and if you are working in 16 bit it just isn't worth the time messing around too much adjusting colour balance and luminosity in the scan software, except as indicated here. By trial and error select the film type that comes closest to believable results without further adjustments. Silverfast allows some fine-tuning of this preset. Use it to improve the preset and keep that recipe. Then for each image do a couple of basic adjustments for mid-range exposure and grey balance (using the grey "pipette"). These measures alone will provide a decent enough result to reduce the severity of further luminosity and colour balance adjustments that will be needed in Photoshop. I have not found a way to automate my way to "perfection" when working with negatives. It is an image by image process and takes time.
Silverfast does accept ICC profiles, so Jonathan's suggestion to make an ICC profile from shooting the GM Color Checker should not be dismissed out of hand - but it does require being able to replicate the film type and vintage effects and "appropriate" lighting conditions - so useful under some conditions, but not others - like everything.
(4) Don't use Silverfast for grain removal or sharpening; they vastly increase scan time and there are much better (more controllable) post-scanning solutions for those two requirements - e.g. Neat Image to clean-up the grain (auto-profiling each image and then previewing the result) and PK Sharpener Pro to recover any lost acutance. Both of these need to be used with care, which will be part of my eventual write-up.
(5) Use ICE at the scanning stage if there are black spots reflecting degradation from long-term storage. It even works with Kodachrome nothwithstanding that Minolta, for example, says it doesn't.
Hope this helps.