I just unearthed the '68 Barracuda from storage and noticed a few drops of primer overspray on my new black vinyl seats (Legendary Int, from Dante). Evidently the interior wasn't properly masked off when the inside of the doors were shot. It seems to be one setback after another with this car, I can't wait to finish it and get rid of it.

Can I use paint thinner or "oops" to safely remove the droplets?

I had the same thing happen with one of my fairly new seat covers. Unfortunately, it seems that anything cabable of removing paint/primer from upholstery is also quite capable of removing dye. Maybe you can redye the seat covers after removing the primer.

Maybe I should "overspray" some black onto those droplets?

Try some naphtha.

I had this happen to me - only the WHOLE interior was covered. Fortunately primer dries quickly and most of it was just a dust. Spray Nine did the job.

use a clay bar with a lubricant like water

I had the same thing happen on my Road Runner (limelight on a black int.) I used laquer thinner and a fine 'scotchbright' pad and it worked. Make sure you apply some king of dressing to the vinyl after, as this tends to dry it out.

I wonder what I did wrong, lacquer thinner on a rag took the color right off the cover. I don't think it even touched the primer, boy was I PO'd.