I guess I'll, chime in here, though I may regret it. (I often do)

If the rating system actually meant anything then your point of it being useful to those downloading the content might be a valid one.  However, because of the convienence factor you mentioned, which is in my opinion a valid observation,m how many of the ratings that do appear would you suppose actually come from people who have downloaded and used the content and then returned to rate it?  I'm guessing it would be a very small percentage.  So when folks are seeing ratings on things at this site most of what they see are as previously mentioned just a person's opinion based on a variety of factors. 

How good does the preview/promotion of the item look when they get here and often, since we promote our own downloads, does this individual have a reputation for producing quality usable free stuff with working files among the users of the refering sites.  This type of rating can be subject to abuse, but if genuinely rated on those factors might be useful to a downloader.

The problem comes from the divergance of opinion among the folks who are uploading content as to what is or isn't useful and their ratings being based on these opinions (to which they are definitely entitled).  The high end 3D user who thinks that there is too much Poser content on the site and sees Poser as useless, if they rate, are likely to rate that content low with no knowledge of the content itself.  The modeler who thinks there are enough textures might do the same.  The 3D person who sees no use for elements of 2D design the same. And on it goes.  

While everyone is indeed entitled to hold and express an opinion, these types of ratings are of no possible use to the downloader looking for a specific type of content because they aren't really an accurate reflection of the content being sought.  And one only need read forums, here and elsewhere, to see that people do indeed evaluate content on this groupline criteria.

When you add to that those who would just blatently abuse the rating system by highly rating something just because they are friends with the creator or poorly rate it because they dislike them, regardless of quality, you are left with the current mess that is the rating system.

Not being able to see this as any kind of useful tool to a downloader, I see no point in the system existing.  Better to police the site for download fraud, work towards getting things properly categorized, pull violations when they are found and let nature sort out ranking by using a sort by number of downloads feature in place of the sort by rating.  Not number of views mind you, but number of downloads, a close look at something is often enough to tell one they don't want to download something for any number of reasons. (unsuitable for their needs or whatever)

I can't help but believe that if one consistently does their best work , provides working files, adequate readme's and documentation and keeps their ear to their respective user base's needs and desires are that  quality will show in the long run.  And it will show in the form of people coming to download those files.  A better and more extensive catagory of searches would probably be necessary to accomodate items that might be seasonal in nature.  But it just seems to me that this would better serve a downloader than a star rating system that is too often based on anything but the content it is rating.

Just my opinion and my observations in the couple of months I have been using this site and creating free content.