Get your score back before you even think of retaking. Like Goro (an adcom member) says, your score could very well stay the same or even drop in such a short period of time. If you genuinely think you will benefit from a little more time, delay your MCAT to the end of August or something.
Sure you could take it 2 or 3 or even 6 times, but taking it once and doing well always looks better. The last thing you want is to retake it and score the same or lower, and then just confirm that you hit your plateau. I knew a girl that really wanted a 35. Her first score was a 32. She then took it 5 more times until she got a 35 (increasing by 1 or staying the same each time). She was crazy. Don't be her. That one time 32 would probably have had the same (if not better) effect application-wise as those 6 32-35 scores.
As far as the MD tiptoeing thing goes, what Goro means is that with a 28, your MCAT will not be the thing holding you back from DO schools. Because of that, gunning for a 30 (a mere 2 point jump that is essentially in the same margin of error as the previous score) might look like you are aiming for an MD acceptance to some adcom members. Now if you get a 26 and retake and get 28, I doubt some adcoms will think you were going for MD (even if you had that intention all along).
You should aim to get your highest score in the most reasonable amount of time, but if you get a 29 and your goal was a 30, I wouldn't take it again. I scored a couple points below my target goal (and multiple points below my average practice test scores), but I just made my "not going to retake" cutoff, so I said forget it.