Exactly, bringing back minor but popular characters does not harm the franchise. If anything it makes it better because it takes the huge potential of these sidelined characters and expands on them. Before TCW Maul was just a brutish weapon of Sidious who did his bidding and then was killed. Now we see he is not an unintelligent brute, he is cunning, manipulative (and his voice acting is great!) and he want's revenge. We're finally seeing the good guys lose, especially Obi Wan who has been owned twice, the second fight was actually quite suspenseful, and Adi Gallia was killed. And we're finally going to see Sidious pick up a lightsaber! I really don't see the negatives of bringing back a character like Maul, who was wasted in The Phantom Menace. (And in the real-world its boosted popularity for the show, and secured future seasons.)
Not sure about Boba Fett, I know little about his EU exploits. But what I do know is his potential was equally wasted in Empire Strikes Back and Return of the Jedi. He said little and did little, his character was not explored at all. The EU is doing that, its exploring and expanding on a character with incredible potential, and giving them a good reason to resurface the Mandalorians. I see nothing but positives... except coming to terms with slightly implausible deaths.
In a nutshell, I have nothing against, and wholeheartedly support the revival of minor characters whose potential was never fully realised. Mace Windu is not one of those characters, and I therefore would not support his revival. And I reject the resurrection of Sidious for the same reasons. Some characters should stay dead, they've fulfilled their purpose. Boba and Maul are not those characters, they have so much more to give.
There is no reason to explore BF. He IS a minor character that fans blew out of proportion. I hope he stays dead in the next set of movies. He may be alive in the EU but as far as LA is concerned, the EU is just fanboy BS that they let people write. The movies are their own canon. (And apparently TCW since LA directly tied them to the movies.)