I matched at a top 5 program with no away rotations. You gain little and can harm your chances as well. If you have good Step 1 scores and decent 3rd year grades, you are fine. You're really not going to impress anyone as a 4th year anyways, much less in radiology where you do very little to start with.
If you are planning on just doing a DR away, there is nothing that you can do that will impress a resident or attending. IR is a different story because you can show some of your technical skills (if you have them). Regardless, I would not advise doing any away rotations unless you are trying to show genuine interest in a program that is either outside of your geographic region or wouldn't think you would want to come there. However, geographic bias really only applies to mid tier programs (maybe with the exception of some Midwest programs like Mayo and MIR). Top programs do not care where you are from, they just interview the best of the best (and therefore an away rotation is really pointless for these programs if you already have good stats). I matched at UCSF this year without doing an away and with no ties to CA whatsoever. However, if you are a great applicant not from CA but interested in mid tier CA programs like UCI or UC Davis, then an away could POSSIBLY be beneficial. Maybe some other applicants from this year's cycle can share their thoughts on this but that's my 2 cents for what it's worth. Feel free to PM me with any other questions. Good luck!