I'm involved in the development of an addon for the Classic WoW versions (Questie), and the thing I do there is such a convoluted process that not doing it feels like letting my fellow devs and the users down. But you can do development on the PTRs and beta servers, so I haven't given money to Blizzard in a long time. Now you could argue that this is even worse in regards to supporting Blizzard than just paying for a game, but I rationalise it to myself with the fact that the newer clients will inevitably be used for private servers just like the old ones were (some already are actually).