I own a WOZ and Hobbit and have played DI. Regarding WOZ and TH if you like/love the themes you're already on a winner. WOZ is still a better all round game than the Hobbit for me, but if Keith does the code justice it could well be a tie maybe even with TH out in front by a nose. One thing Hobbit has over WOZ is that you instantly know where you are in terms of the overall mission (collect runes/arkenstone modes) just by looking at the screen. I also love TH's drop targets and the accuracy needed, over WOZ's mini playfields.
Regarding DI it gets complicated... I would say you have to play it to decide if you like the theme as it's kind of love/hate thing. I was somewhere in the middle, it was a really fun game, the theme was ok but I'm not sure if I could justify the money if I don't love it. "Shoot the right ramp to charge phone" and all that other techno/kitsch stuff doesn't do anything for me. A better theme and I would have been all over it like a rash. I would give it a good play if I saw it on location but not to own.#
Good luck - and make sure you play them all at least once before making your decision.