All 3 of these are nice and early, authentic samples. Comparing these to the items these guys sign today, I think you would be shocked at how their signatures have devolved.
I've seen some terrible Mayhews from recent conventions and I understand Bulloch can get shaky at cons, too. Hadn't heard anything about Warwick Davis' sig degrading, though. Really glad these seem legit. As far as authentication goes is there any difference between PSA, JSA, or Beckett or is it just a matter of preference?
First things first, I don't see any reason at all to have these authenticated. Save your money and put it towards the costs involved in replacing the pieces you stil want in your collection.
As for Warwick's modern autograph from the last 15 years or so, some are as short as WD, while others may have an extra letter here or there like WkDs .... samples below
I do see the difference. I probably won't worry about getting these authenticated unless I decide to sell at some point. I have some other non Star Wars sigs I've gotten at conventions over the years and I've grown quite fond of the 11x17 (for dual and triple sigs) & 11x14 (single signer) formats. I'm completely in favor of saving the money, though, as some of the pieces I'm going to looking to pick up won't be cheap.