i am currently rotating at a "top notch" program that includes over 30 residents. not a single one took a year off for research. though, strong academic, research oriented departments with abundant funding may seek out such applicants. these programs are often thought to be soft clinically. some programs may even look at a year off as a negative thing.
as is often said, research is mostly something to have to talk about during interviews. it offers little to getting an interview or rank lists. that said, it is a good way to meet some people and maybe get a LOR.
lastly, not sure what to call it, but doing research to get into residency (with no real interest or plans on continuing to do research once in residency or go into academics) is disingenuous. you may have to outright lie in your interview if you are asked if you plan to continue your research (cause after all, you can't say, 'no, i did it b/c i thought it would help me get into a program).
my advice... if everything on your app is 'fine' and you dont have a sincere interest in research, dont do it.