Wrong forum, but I'll answer anyway, I'm feeling generous and know quite a bit about eBay. That's my main area.
To answer your question, SEO does matter for eBay, however increasing your conversion rate by making your listings more professional is a much better option. I'd reccomend going to
this page on eBay, and setting up your keywords at least.
I've done a few experiments trying to rank eBay shops for certain keywords, and have had some success, although as stated previously, I'd focus my main effort on increasing the listing quality.
The best way to do this is to get a decent quality listing template. I actually offer these, and you can check them out
here. You can now check out some awesome statistics about your listings with the new 'Applications' tab from My eBay, be sure to check that out too.