I'm not sure Capaldi was as maligned in the role as Colin Baker ever was. Heck, I don't think anyone was ever maligned in the role like Colin Baker was. He never showed the true extent of his Doctor's breadth, never had a solid classic besides Vengeance on Varos, and even then arguably so, and he was fired from the job. From the sounds of it, Capaldi left on his own accord. And, he did get to play a lot of different facets of the character, developed him quite a bit in a way that Big Finish can certainly expand upon. But what BF did for Sixie is continue to evolve him, mainly as a way to bring Colin Baker (and thus, the other Doctors), giving Sixie a kind of run he never enjoyed on TV.
Of course, what they did for Eight goes without question. He was hardly defined by the books, with only the comic strips having any indication as to how that Doctor should be.