You gain much more than a potential publication from meaningful participation in research.
1. You gain an in depth understanding about a scientific topic that interests you. This dedication shows enthusiasm for science and intellectual curiosity.
2. By participating in research you show your ability to juggle several demanding responsibilities.
3. You learn to work as a part of a team. You learn to communicate with people "below" and "above" you effectively.
4. You gain critical thinking and reading skills from understanding how to read scientific articles and how to extract information that is important to you.
5. You learn to problem solve. With a proper research experience you will hit roadblocks and failures along the way. Not only do you learn to not get bogged down with the problems that arise, but you also learn skills to overcome those problems.
6. You are empowered with the ability to understand where your education/skill set is lacking and you have experience with asking for help.
7. You learn to differentiate a problem that you can solve with hard work vs. a problem you ought to ask for help in solving.
8. You learn to identify sources that can help you and you learn how to appropriately obtain the help you need.
9. You show commitment and follow through if you participate for a long time.
10. You gain an understanding of what it is like to participate in research and can start to figure out whether you will want to be a physician scientist.
11. You gain effective presentation skills - posters, oral presentations, journal club presentations, presenting your progress to the PI etc.
..... The list can go on and on.
Edit: Bottom line - if you can articulate your growth as a scientist/student/person as a result of participating in research, you will be successful as far as applications go. If you can articulate the science underlying your lab's research and seem enthusiastic about it, you will come off well in an interview.