Doing an away elective at the program of your choice in California is probably a good idea. Apply early for those aways -- I started eyeing a list of electives around December of M3. Then I sent my earliest application in February. (And give yourself 2-3 weeks prior to the deadline to gather all the appropriate materials -- transcript, photo, letters if required, etc). You're probably still safe if you apply in March; by May or June I'm not sure, they might already fill up with students.
My feeling is that most programs will strongly consider offering you an interview (even if they don't offer it automatically) if you have done a rotation with them -- particularly if your application is at least average as a whole, and above average in some way.
Having said that, choose a place that you think you might LIKE before you do an away with them. Don't just go by reputation. If the pgrm has a great reputation but students basically get ignored by the faculty, you'll have a hard time asking for a LOR if you need one. If you've researched, asked around, read Scutwork.com reviews (etc) and the place sounds like you don't want to be there, be cautious about going. Pay attention to the reviews of students who rotated there, as well as those of residents. Why? Because you're a student now and how students are treated during their rotations gives you an idea about whether it's a good place to rotate at. Nothing is worse than wasting a month of getting up at 5am and working your butt off, and spending the money on travel and accommodations, for a program that you decide you don't even want to apply to.
