Schools will not view your decision to dedicate an entire semester to preparation for the MCAT favorably. I had a discussion with the admissions coordinator at the University of Florida COM and was told that I would be expected to both prepare for the MCAT and fill my spare time with additional activities. If you dedicate all your time to MCAT preparation, schools will expect phenominal scores.
If you don't take classes, you should at least involve yourself in numerous EC activities. Essentially, you want to try to simulate the life of a med student (schools want to see that you can both work/study and excel).
I was in the same boat last year. Things are looking better. Good luck!