What I do is to dust the slides before placing them on the scanner's tray, then remove any remaining dust and scratches using photo-editing software in my computer. But VueScan uses a very good dust removal algorithm.
I haven't scanned ay of my slides for over a year now
Here's a comparison I threw together several years ago with a random negative from probably 2007ish taken on Kodak 400UC(a negative and not a slide, but the comparison stands). This was most likely processed by a Walmart on-site "One Hour" lab and I picked it because it has a nasty scratch and I like the composition enough that I think it might have potential if I wanted to massage it.
Don't remember the exact equipment, but a Canon New F-1 with a 50mm f/1.4 would be a good bet. It was plenty sharp.
First of all, the negative with no correction on the Coolscan V in Vuescan
I'm going to pay particular attention to an area on the truck back window since it has a prominent scratch and several dust spots.
First of all, a crop of that area with no correction
Now, Vuescan with the dust and scratch reduction cranked up to high
Notice that while both the scratch and the dust are reduced, they're still there.
Compare that to ICE from Nikon Scan
A couple of the bigger dust spots are still visible, but the scratch is gone completely as are the smaller ones.
BTW, wet scanning can basically eliminate the appearance of dust and can minimize scratches. I've wet scanned on my V700, but it's royal pain and it's even more frustrating when you see a bubble you missed.
Also, as scan prep, I typically use a Pec pad with Kodak film cleaner(the nasty stuff that works amazing) and then use canned air to make sure. Still, though, dust is a persistent enemy and you're probably not getting rid of it unless you're in a clean room. As I mentioned above, paper slide mounts are probably the worst about this, and when I use a lab that I know uses them I request unmounted and hand mount myself in plastic(I need to fix my Coolscan IV and get a roll adapter for it so that I can scan a complete roll before mounting).
Is this splitting hairs? Maybe, but to be happy with the Vuescan output I often spend twice as much time in Photoshop healing and cloning as I would a direct output from Nikonscan or Epson Scan.
I have an Epson Scan comparison around too that I can post...