Larry - great idea. I bought an add on like that for a Nikon point and shoot and used it in the past. Kept that camera because I have a number of unique accessories for it like that.

The dust will show up no matter whether you scan or shoot the images, so invest in canned air and a good slide brush. Small cost compared with the improved results.

Those slides that have have color shifts (usually the reds fade out) can be renewed using a program like PhotoShop (the simplest $99 version will do this kind of improvement).

Finally, after scanning the slides, it would be a nice idea to store them in acid-free containers. No sense putting them back in trays - when was the last time you projected them?

All well and good - but unfortunately my oldest slides from 40-50 years ago were lost.