Late to the party but i wanted to give my two cents. I've dealt considerably with carded and boxed action figures. I can only tell you what I would do (and have done). And of course, suggestions are dependent on how much you paid for this collection.
I think it is worth submitting the Bossk, Vader and Kenobi to a grading company. By the way, Bossk is hot and this one is on a ESB 32-Back card! Much like CGC slabbed books, the figures will command a higher price and if anything, will sell faster. I do think that another factor for graded figures selling better is that the submission process is a bit cumbersome (and expensive) such that customers would rather have it already taken care of for them.
I have exclusively used AFA as I think that, out of all the competition, they are the most reliable and right now, realizes a better ROI. I just wish they would modernize their website and make their online submission process more streamlined (I have been offering to do so for years now!).
I won't speak on the casing / yellowing issue as @Comicdey did a great job explaining it, much better than I could.
And congrats on this very nice vintage star wars pickup!