It is very difficult for me to tell given the broad range of undergrad involvement in research (I washed things once a week vs. I work 20+ hours a week on something I think is awesome and know a lot about and everything in between) how much of the "I had research in undergrad" crowd on MSAR were just students completing a self-fulfilling prophecy (research gets you into medical school and therefore I did research) while doing everything else well enough to get away with 0 research. My intuition is that the percentage of people who received a leg up precisely because of their research background is actually very small. At most I believe adcoms value understanding how to engage with primary literature and the scientific method rather than man hours spent looking into the microscope. Barring MD/PhD committees, of course.
Just excel in every other category and you should be ok. Scholarship is important but research, the scholarship of discovery, is only one kind.
