What do you mean worth? Like, in money, or at the bench? If it's the former, not much. If it's the latter, plenty.
It actually surprises me how little these go for on the used market. That's why I got one in the first place, and probably why I still have one. I paid damned little for a used one many years ago, and even though I don't use it as much as I should, there's no way I could get a price that would justify my selling it. I have several vises that I use for different, specific purposes, and my Regal is often the odd man out. But, if I could only have one vise to do everything, the Regal would be the one. I think that's a pretty good reason to hang on to it.
If you're looking to sell and someone offers you $100, I'd say take it. If you're looking to unload it quickly, I'll give you $50 plus shipping.