I am a tikiwiki novice, I have now started creating themes. I will
1. copy files
2. modify files
just like every theme creator does. For instance, I pick one theme with an odd 30 colours, history unknown, and modify the parts I don't care about to end up with 33 colours. Result: yet another theme, only more complex, there is not any obvious relation with the appearance at different ends of the wiki. The old css-files were almost unreadable, and the new ones are worse.
I wish the theme definition process were less complex. There are many ways to obtain that, here are a few ideas.
METHOD 1: Separate the definitions of fontfamily from fontsizes from colours from other elements. One file defines fontfamily, the theme just reads that file, and reads another one controlling colours etc.
METHOD 2: Seperate the different parts of the wiki, e.g. one file controls blogs presentation, another controls forums etc. (This is not the same as what is called Theme Control in Tikiwiki, naturally.)
METHOD 3: Something similar to the preprocessor directives of the C programming languages (who can live without it) would allow you to reduce the complexity considerably.
- and you might combine these ideas, there are probably many more ways.