Yeah, I did ask what nicely designed means. Design theories, as you mentionned, is one great answer. Having all related resources for that in this thread just feels a bit too much for the context of the original post.
A discussion about criteria for nice design (along with the related resources) could make for a right interesting separate thread of discussion.
Thing is, folk can look at something and think it is wonderfully designed, and the thing doesn't follow at all general theories of "good design" All of the research in "good design practices/principles/theories" don't matter much when folk like something that doesn't follow any of it. (That's when new "good design" practices/principles/theories come to light, which may be evolution or just latest trends/fashions/fads.)
Pretty designs can turn into awful when the design doesn't follow good practices. For example, folk think something is the prettiest thing they've ever seen, but the thing has hidden interfaces (i.e. interfaces that only appear upon mouse hover or something else). Hidden interfaces are brutal.
The example you give is interesting, very unique, cool in a way, very creative, and I want to run away from it because I find it hard to read.
Showcase TiddlyWiki's are like marketing. Who are we marketing to? And what are we marketing?
If we showcase "nice designs", non-technical and non-designer folk might get the impression that it is easy to have that design in their own TiddlyWikis. If showcasing designs, it would be awesome for each example to have a plugin so users can have a TiddlyWiki that looks exactly like the one showcased, along with easy ways to customize and make their own. If the nice design can only be had by those who are technically proficient and have the time, or by those who can afford to pay for it, it can be a little disheartening for those who are not techinically proficient, and/or don't have the time, and/or can't afford to pay for it.
I'm just thinking TiddlyWiki level of aliveness via level of nicely designed is problematic. Showcasing TiddlyWikis based on whether or not they are nicely designed is problematic. (Who decides, why would anybody submit cool TiddlyWiki solutions to problems if one thinks a solution will not pass the "nicely designed" test?).
But this is all a strange discussion (yeah, I'm going in circles) because I"m still not really clear on what problem we are discussing and how "well designed" ("pretty" is just one attribute of oh-so-many) addresses the problem.