I think retaking the MCAT involves a lot of personal reflection and thinking about your study skills, time, etc.
Some questions that I would probably reflect on...
1. Why do you think your score was low? Did you cover all the material well? Did you spend enough time covering all the topics? Did you do tons of practice tests? Did you follow your study plan? Were you satisfied with your studying before you took the exam and received your score?
If you can identify "reasons" why you scored low, then they would be easier to change.
2. Did your practice tests scores reflect your test day score? If not, what was the difference? Were you getting 27-29 on the practice tests and got a 27 on the day? Were you getting 33-34 on practice tests and got a 27 on the day?
3. How will you change your study skills to increase your score? If what you did before didn't work, then logic would suggest trying something different. However, it is hard at times to really change your plan.
4. How is the rest of your application? Students who are white, have an MCAT 27-29, and have a GPA 3.8-4 have ~61% acceptance into medical school. Do you have a strong GPA? Unique or strong ECs? Or is the rest of your application just okay?
5. Do you have enough time to dedicate to studying to ensure that you score higher (30+)? If you are in school/work, do you have enough time? Really, do you have enough time? {This is why I decided against a retake. I was in grad school and didn't have time before the next cycle}
6. Do you think you can really increase your score to 30+? I heard that scoring the same is way worse, because adcoms expect improvement. You have to show that your 27 was an error, and it is hard to show that if u score the same.
But.... with that said... 27 is low. At most MD schools you will be below the 10%. You are entering a very competitive process with a score that is very low. With competing against 1000's of students, why should they pick you?? You want to put your best application forth, apply once, and get in.
I love this specific thread, because it is supportive. You see people who have low MCATs getting into medical school. You see their passion and commitment to medicine. It is exciting. However, it is exciting for a reason. People don't expect at times individuals with 27-29 MCAT to do extremely well in their apps. I would say that people who found success might be the exception rather than the rule. But, it definitely is possible...
Summary: If after reflection, you think that you really, really, realistically think that you can increase your score, then do it. You would be in a 10000% better position with a higher MCAT.
That's just my two cents. But, I don't really know anything.