i guess it depends on what you mean by The 'Quality' Of A Site.

a site's quality is more than its content, although content is king. but the layout of a site can greatly affect retention, and i would consider that to be part of the quality. showing the updates from the main page, having news items about the site on the main member page - those things i might consider part of the quality of a site. also plugins that actually interest the members of that site might add to the quality.

and members do care about that. also i've seen bad tours get facelifts and improve their sales 100% or more, and often 50%. and i've seen sites get turned from a stodgy old standard tour into an attractive reality tour and have sales go up.

and i know one network of sites that has THE worst design of pretty much any sites i've seen - and sells terribly. on the other hand, the content is supreme, so it retains depsite its member area layout.

so to answer that, i think defining quality is important.