I think the money paid to some developers is an excellent investment in them and their desire to improve on it / maintain it. WoW and HB are updated a lot so the existing products often need a lot of rework. An HB dev with items on the store has to commit to an 18 month support contract of sorts I believe. Devs like Studio60, Millz, Brodieman and Tuanha to name but a few (and by no means is that list comprehensive so apologies if I didn't give you a 'shout-out'!) are excellent in their support and work ethic.
I have been stung by some products not working or being supported - Akatosh Quester (eu29.99), Garrison Butler ICE Edition (eu24.99), Templar (eu12.99), etc. etc. and there are those that are no longer relevant like Ultimate Ashran. That said, I do have some disposable and this is a minor hobby in my life. HB has caused my account to be banned, but that's a calculated risk I was willing to take as I would have given up on WoW years ago otherwise.
Lots could improve and hopefully will. Overall I do support the model and see it is probably the only way a game with a slowly dwindling player base and a bot with the same can keep going and incentivise the devs to stay.