Do they actually have a free version these days or is it still Sculptris? I remember being so mad when they grabbed that and then did nothing at all with it forever.
I've found 3d improved all my skills in the things you're hoping to improve so I hope that works out for you too :)
Though I hope you actually also keep improving at drawing as that completely eluded me, I cheat there and draw over my bases coz my 3d is a lot better than my 2d XD
zBrush on iPad has a free version, I'm just switching to different things then setting myself up to regret and should've just focused on one thing to get things done because that's the right thing to do~
Sometimes you need to jump around between things til you find what you want to focus on, because sometimes what you think you want to focus on is not it, and interests will wax and wane and go, and it's all good if you learned something, even if it was "this is not it" :)