Yeah, Light has lost most of his appeal...now it's mostly just hoping he gets his comeuppance.

Sayu/Matsuda hasn't evolved really(I guess it's too cute and fluffy to get much attention in the manga?) But it's clear that he has a crush on her(that's probably at least somewhat reciprocated, however innocently) and that both Light and his father know and aren't sure they approve.

I actually really wish we got to see more of Sayu. She is, I think, the only person Light actually loves, and adds a much needed degree of humanity to him.