I have no problem with licensed theme brickfilms, as long as they're done well. That's basically my rule for all brickfilms, whether they're original property or not.
The only issue is that with the rise in the popularity of brickfilmers like Forrestfire101, filmyguy and most recently Brotherhood Workshop - all of whom I hold in high regard - YouTube has become increasingly saturated with people trying to copy the formula, and by people I mean (and this is probably going to sound mean) kids who take 20 frames and expect to get thousands of views. For ages, that gave licensed theme brickfilms a bad name here on BiM, and I felt awkward trying to do a Batman brickfilm when there was such a negative reaction.
As far as viewing them goes, I tend to stick to animations I know will be technically impressive, such as those by Forrestfire101, while I go to other brickfilmers for originality and characterisation. Brotherhood Workshop's animations are breathtaking but simple; they're enjoyable, but still not a patch on something like Unrenewable.
I personally am currently working on a series for BrickUltra called Avengers Tower, which is basically just a chance to put my collection of Marvel minifigures to use. I also plan to resume my Young Istari project at some point, from last Halloween, which is a bunch of short-but-sweet Tolkien parodies. The reason? Well, like any hobby, brickfilming is about working on projects that you want to work on. While I have lots of scripts ready to animate that are original stories and characters, and I'm champing at the bit to get them made, I also really want to do a Spider-man animation, or an Agents of S.H.I.E.L.D. animation. It's not something I can easily explain, but I think it's for the same reason I bought the sets (and the additional figures that I found on ebay, most recently Loki and Eric Savin) - the appeal of having a LEGO Iron Man, or Thor, or Batman, or Luke Skywalker, or Captain Jack Sparrow. Brickfilming's only an extension of play (in a sense) so it's only a logical step to go from buying Batman LEGO to animating Batman LEGO.
Doing it for the views is something I'm a little bit guilty of, but I wouldn't even be doing that if I didn't enjoy making IP animations. I've been doing Avengers Tower for another channel and it's got more exposure than it would have done on my account, which is great (just over 3000 views in two months is good, for me). Ideally, I'd love it if the series could bring in more of a viewership - hook people in with the stuff they're familiar with, like Captain America, and then they'll be interested in watching some of your other, original videos. My most viewed video was about four years ago (I think) - a Green Lantern animation that raked in 200,000 views, so it's worth thinking about if you want to be noticed. However, I would strongly advise ever making a brickfilm solely to get viewed, as that way lies disappointment and the animation itself tends to be bland and, well, it's just not the right reason to be making a brickfilm.
Like any hobby, it's important that you enjoy yourself, and if doing the odd licensed theme brickfilm - or entirely licensed theme - is what you want to do, then go for it. I do, and I love it. To me, there's honestly nothing wrong with doing a Star Wars or Batman brickfilm if that's what you enjoy. For me, it's a way of havign fun animating, let's say a fight scene, in order to hone my animation skills, without having to worry too much about prior characterisation. Plus, the odd reference, bit of name-dropping or even frame replication from the actual movie can be quite fun.
All this coming from the guy who started the no-licensed-theme BrickFilm Cinematic Universe #lol . I plan to continue with all of that alongside licensed theme projects: up soon are vampire owls, more conquistador adventures, smiling demons and a genie.
EDIT: As for whether it's beneficial to the hobby overall...like I said, YouTube is saturated with kids whose only interest is to copy popular brickfilmers or do the odd animation and then stop. In terms of creativity, it can be detrimental, as a lot of the time licensed them brickfilms can just be shot-for-shot replications of movie trailers or clips. Though many are done well, a lot are not and also don't encourage any kind of creative writing ability.
The balance could be to use licensed characters but then build a story from that. I'd like to cite some of Atlas Animationz's work for that - the guy's done a series of Marvel brickfilms that may be predictable in parts, or quite simple, but the dialogue is mostly pretty strong (Spider-man's feels like it's straight out of the comics) and I was really hooked on later episodes. Overall, what he's produced is a lot more interesting than a "trailer done in Legos", and this kind of brickfilm would, I believe be beneficial to the hobby. It's got the familiarity to draw viewers in, but it's a story into itself and is well-made.
Atlas, if you're reading this, I want to know who voices Tony Stark in your videos.
That is all.
"Nothing goes down 'less I'm involved. No nuggets. No onion rings. No nothin'. A cheeseburger gets sold in the park, I want in! You got fat while we starved on the streets...now it's my turn!" -Harley Morenstein