Aligning the stack at runtime is one instruction in the preamble so it's not a big deal, especially if the function is big enough to have non-register SSE locals.  Also, when using VLAs, it's not optional.  I use SSE all the time and have no problems with the alignment requirements, but it's not really a performance issue and I'm doubtful that it was worth the time for people to learn and deal with this idiosyncrasy.