Let me preface by saying I have never gone from BWI to FW (so why am I responding???
). But seriously, I did stay at BC in 2008 and had to get to the afternoon tea at GF. We did the 'free' transportation. Since we weren't at MK that morning or going to be there for the evening, it ended up taking so long to get there and back (and we tried two different 'free' ways). It took the whole hour and a half to get from one resort to another so a total of 3 hours traveling
So the lesson I learned was that I should take a taxi from resort to resort if they weren't in monorail/boating/walking distance of each other. I felt like we spent so much time on the transportation that we really lost out on time we could have been at the parks or the pool. So there's my two cents for what it is worth. It is worth the $15 to get a ride directly!