First year: still settling into university, respectable 3.5
Second year: bombed Ochem, genetics, etc. still recoverable
third/fourth year: no more joking around, straight A's.
I have similar gpa trend, consensus is not to waste money on SMP/post-bac. 3.67 is still a very good GPA and like you said raising to 3.7 won't make much of a difference. If you have a gap year, just try to strengthen your app through other means: work, research, shadowing, volunteer, rock the mcat, etc.