Oh geeze, I guess I opened my mouth too wide :-) Being a programmer, though, and not a graphic designer, I often can't come up with good designs myself, I guess I just know what I like if someone shows it to me. However, for me, its not so much that Im not overly thrilled with the current themes, I think its there are some common aspects that I dont care for, and am always editing the css after the fact.
I would probably lean tward more gradients and rounded corners, and less padding. One thing I always end up removing or reducing is what I consider is excess padding inside of all form elements, including buttons. This is a pretty minor inconvenience I guess though, and you should create styles that the majority of your users prefer.
One suggestion I might make though is how you skin your objects, and apply those skin styles.
Currently a login page created might have a form that starts like this
<form class="Basic_Default" id="LogIn_Basic_Default" name="LogIn_Basic_Default" method="post" action="">
<fieldset class="Basic_Default" id="Log_In">
In this case I chose the basic default skin.
Personally, long class names like this drive me nuts, and they make changing a skin later difficult.
I would prefer if you gave your classes and IDs more generic names like waProgressWrapper or an id like waLogin etc. Prefacing the class or ID with a brief 'wa' to differentialte it from similarly named generic classes we might already use.
You can then have your skins, or themes in different directories with master css files, and then you can just attach a different stylesheet to totally change a theme.
Or even have a master stylesheet, and then pull a theme into that stylesheet with @import.
Putting all of your extension includes in a single includes folder (or in your case webassist folder) was something I pushed for a couple years ago, and I am glad that has been implemented. It really helps tidy up a site.
Anyway, a little more that you probably wanted, but I wanted to express my opinion.