Speedometer 3 is in the works, and it's moving in this direction. On multiple occasions we've done performance analysis of the latest draft version, noticed a particular chunk of code is hot, considered what it would take to optimize it, and then changed it because we don't think it reflects real-world usage.
EDIT: And I guess the answer for "why not fix SunSpider specifically?" is that once you've done the work to turn it into something worth optimizing, it no longer bears any resemblance to the original. It probably looks a lot more like Speedometer, honestly.
I get that, yeah, but superseding the old name is probably worth it though; the internet is full of people who never get the memo except via version numbers :)
I tongue-in-cheek proposed that we match the Sunspider ASTs in V8 and either make it infinitely fast or infinitely slow. Now that will kill a benchmark once and for all!