The benefit you get depends on how good or bad your room is to begin with. Some people are fortunate to have really good rooms from day 1, ie they made lucky or appropriate choices in dimensions, floor and wall finishings, drapes, bookshelves, wall hangings, furniture and choosing flabby, sound-absorbent friends
If your room is pretty good already, and it sounds like it might be, you won't see the same obvious improvements from randomly adding room treatments that you would get in one of those "rooms from hell" that some people end up starting with. You need to be much more selective with the treatments you choose in order to get value from the investment.
I wouldn't rush into room treatments if I were in your situation. First thing to look at would be clarity of imaging -- you probably have much more absorbency on one side of the room than the other courtesy of the drapes -- but if your imaging seems good (play some recordings using just the mains and see how clearly the different instruments can be located between the speakers) then I would just kick back and enjoy.
