I have the Von Stavenhagen sights on all of my classic Sig pistols. I prefer them over the two dot rears as I can acquire my target quicker and work better with my vision. Plus they are what I know.

Long story short are there any practical reasons not install #8 Von Stavenhagen sights on my P238 and P938 pistols?

They are a bit hard to find these days, but other than that, no reason not to.

I've always preferred bar-dots over three-dots myself. Guess I'm just old school. But even better for me is just a post in a notch, and no dots at all.

Were VS sights even made for the P238 and P938?

No, but the rear sight cut (dovetail) is the same as the cut on the classic Sig slides.