If you're only planning to do research for one year, you'll just barely be starting when you submit your app, meaning you won't be able to write much about the experience or get a strong LOR from your PI. I don't think it would improve your chances at any school unless you've already been there for some time.
I'm a CRTA at the NIH, and I think it's great, but I haven't done research at a top 15 university, so I can't really compare the two.