Right, but thinking of the forum itself as an expression of the creators' personalities and ideals, sort of cause its design and layout to attract certain types of people that create that personality. It is a big part I think, and it is something that communities can lose out on just by using a theme that doesn't properly convey their own ideals or identity (which using a premade theme it never will be exact).
That's not to say that you cannot have a forum or community with its own identity by using a theme selected from a list, but it does take away from the level of uniqueness and personality a site can have, and in a way does detract from forming such an identity.
That's understandable, seeing as both Forum Advertiser and Wober, two relatively successful forums of yours, have, to be perfectly frank, looked quite nice.
I think themes can be overused.
Just imagine every website on the Internet having the same exact color scheme and layout.
It'd be boring. Every time I browse a forum I want to see something unique so I actually have a reason to distinguish it from the others.
Now out of all those forums that have the same theme, would you join a forum that has no posts * or a forum that has thousands of posts? 😉 I wouldn't necessarily join a forum that has thousands of posts if I don't like the content. If a forum has no posts *, but the content is to my liking, I will join it. The theme is the last thing I look at when joining a forum -- of course, if I can't see the links because it's too dark or it's just too bright, I wouldn't join.
* By saying "no posts", I mean a forum that has only a few posts (maybe 50 or 100), and a few active members.