This is a lot to read, so you might get more advice if you find a way to shorten it a lot. I think the best way to improve your programming skills over the sum

This is a lot to read, so you might get more advice if you find a way to shorten it a lot. I think the best way to improve your programming skills over the summer is to program a LOT; just work on open source projects that you find interesting, and maybe start a few of your own. Learn some new technology you've been curious about (languages, operating systems, version control systems, and so on). The advantages of being in Silicon Valley are going to be marginal, compared to the advantages of getting more practice/experience and learning more. Maybe someday it'll be worth heading out there, but I'd guess it wouldn't be worth it right now. (But don't let this advice stop you if that's your dream, or something.)