Even if you don't build...

..be an informed consumer. You'll be better off for it, and so will Second Life.

Read the "Topology - the often neglected entity" thread in the SL Mesh forum. It describes the process builders go through to make efficient meshes that work well with animations. Codewarrior Congrejo does an excellent job of explanation, with illustrative examples and images. Note especially this point: just having tons of polygons does not make a garment high quality--in particular, it doesn't mean that a garment will track well as your avatar bends or moves its limbs.

If you are into digital photography, you may have read about the "megapixel race" and how megapixels aren't the sole measure of quality of a camera. In the very same way, and also just as it doesn't make sense to always use high-resolution textures (you've read Penny Patton's article on how huge textures applied to tiny objects needlessly make frame rates plummet, I hope), polygon count isn't the sole measure of quality for a mesh. Over in the JIRA entry for the mesh deformer, people have expressed concern about the issue, vide this from a comment there by Jesseaitui Petion:

I'd like to respond to a comment made a few times here already, about designers making high poly content because they are "inexperienced". That's often not the case at all. Many designers are purposely manipulating their content to appeal to the "inexperienced" consumers. Consumers don't understand "high" and "low poly" in the way you and I might. Many consumers won't touch a low poly model with a 10 ft pole because it looks subpar to high poly models (I'm referring to the clothing market here). Consumers don't understand that these models may lag them. What we see as "unneccesarily high poly", they see as "this content came from a skilled and advanced designer." What we may see as "good modeling, low poly" they see as "jagged outdated content from a subpar designer." One makes you money, the other doesn't...ultimately the fashion crowd will create what sells. On the other hand, there definitely are people who've no idea what they are doing and subdivide the mesh over and over when no change in appearance even occurs. But just know that a lot of the top designers in sl are high polyin' it on purpose, knowing full well what they are doing.

Please, be an informed consumer. Ask sellers how well optimized their mesh products are. Ask reviewers to provide the information that will let you decide--including photos of the model not just in graceful runway poses, but also in poses that show how items work when the body parts they cover move or bend.

UPDATE: I asked over in the SL Mesh Forum how one can be an informed consumer, and Codewarrior Congrejo kindly responded, suggesting the following (I summarize):

• Wireframe (ctrl-alt-R toggles it) is your friend. Get demos if they're offered, wear them, and turn on wireframe. Then you can see whether an object is built efficiently.
• Performance tools show useful information.
• Develop > Show Info > Show Render Info (toggle) will show triangle count ("tris").
• Read reviews.
• Read store ads; some brag about their wares' high polygon counts.

Follow the link and read it straight from Codewarrior, who is a far better explainer than I am.