You can do them weighted with a dip belt, no?
A few years back, I was doing workouts with bodyweight-type stuff at the top half followed by free weights. I progressed to 3 plates (for about 4-5 reps) so ridiculously fast that I thought I was the shit. And people in my gym were constantly congratulating me because a lot of people couldn't even do 4-5 regular chins. Also, I'm a decent sized guy.
In retrospect, I don't think it was as impressive as I felt it was at the time. I have a theory about why deadlifting is overrated and it applies to chins to a certain degree, too. You engage so many muscles in deadlifting that you can compensate for a weak point in your lift without really gaining strength like you would on most compound exercises, back or otherwise. Chins are a back and arm exercise, but they also engage abs, legs and chest in a way that seated lat pulls don't. (You're probably saying "if you use legs to do chins, you're doing them wrong", but even doing them strictly, there is a degree of body motion that you use to complete a rep. The more difficult the rep, the more you use. Check out the leg movement on the guys in the video posted upthread.) I think chins can do a lot for your strength and physique, but I think there's a limit to how close it will get you to a bodybuilder-type back, even with added weight.
I didn't make this a booklength post, as people have complained about those from me in the past, but I can imagine that anyone who is interested probably sees some things to pick apart. Feel free. I have some other examples and observations that I'm sure won't change anyone's mind.