Porscha.
I believe the main thrust of your question was why are well known (box office generating ) actors and acteesses used to play the various Gay/TG/TS roles. I would have thought the answer was obvious. That the studio bankrolling such a movie/film wants to ensure that it gets its money back from investing in said films.
The result no doubt is that many who would not ordinarly consider going to see such films will do so because their favourite GUY is playing a role that they would not have expected to see him play.
The reasons on top of that may be curiosity,inquisitivness etc.
For the actors as has been mentioned they get to do something, a role that they would net get the chance to do often in their career so showing their versatility to casting directors.
For the big studios they get a return on there investment so are more willing to consider deleoping and then putting into full production a fim touching on areas of society that the majority would most likely never encounter.
To me it does not matter too much if some find it titilating,a laugh or even if they get to poke fun bu watching such films. What is important is such subject matter gets aired to the masses may get them talking about such issues may even get them sympathetic to certain sections of society they may not have known much about.
If such films were not made by the big major studios who would make them ? the independants who may never get any major national screenings in any country. Another film left up in some archive some where.
I wish I could remember the title of a film but one that was made by british film makers staring Julie walters and based on the true story of a city of london stock broker who was having issues about his gender think it was called "Gerald or Geraldine" was actualy very moving and delt with the subject in a non sensationalist way was just a very personal story that was given total dignaty and respect considering the subject matter.
The more exposure given to such subject matter does lead to both greater exposure which leads to more discussions about such subjects between those who go and see the film.
Once years ago I used to get upset at total misrepresentations in various fims TV dramas etc. Now I am not so sensitive about such Films and believe in the long term such exposure will lead to more films being made over time that move with the times and reflect societies aceptance of such diverse groups as Gay, Transvestites and transpeople. Just compare how such material is handled now compared to say the 40's when such subjects was in there for the humour factor.
So I say long may the subject be covered in fims,TV,Plays,Novels biographies etc.
If these subject matters was never covered or aired by such mass media (exclude the tabloids here please) we would still be underground undercover and bigger jokes than I see such communities now seen.
flowering into the woman I always was.