Yeah, it's not like life stops in-between YC rejections. I applied to YC 4 times between SFP2005 and SFP2008. In the meantime, I redid the backend for a 100,000 user website, wrote one of the top Haskell tutorials on the web, launched 2 products for a financial software startup, founded a company, pivoted said company 4 times, watched said company die, ported Arc to JavaScript, and learned a whole lot about programming, startups, and myself. I did eventually have a chance to be a cofounder of a YC startup (not by applying the normal way, but because PG put me in touch with one of the applicants in SFP08 that needed a technical cofounder and they offered me 20% of the company), but by then I'd realized that it wasn't really what I wanted at that point in my life. If the need arises, I'll apply again, but by now I've realized that my drive is to innovate and I don't care whether that happens in a big company or a startup.
I'd like to think of YC as something like the SATs, APs, or patent applications. It is a credential. It makes life easier for you in the future. Pick it up because you're ready for it and have already learned the skills you need for it on other more worthy projects, but don't make it your life's goal. Once you do that, it's only a weekend's worth of work.
That's a good point; I don't. I assume not, though, because I view YC as a program for those without much experience. Otherwise, one wouldn't trade so much equity for being but one out of a huge crowd of YC companies.