I think sigs can look fine with or without CSS. I've seen a lot of sigs without CSS that still looked amazing. Really, I think the usual centerpiece image plays a huge part in how a sig looks, just like how formatting is also important (which often looks cooler with CSS).
But yeah, your sig is great! I'm particularly a fan of the CSS-free formatting.
But yeah, your sig is great! I'm particularly a fan of the CSS-free formatting.