I like the marker idea, Charlie. Markdown tables (or wikitext tables) are such a pain to edit that I have been repeatedly quelling an urge to write separate tiddlers for each row of the one I'm writing (documenting for myself which macros do what, and where they live, in a personal plugin). It's so tempting in TW to write a "solution," thereby opening yet another set of parentheses before I finish the task at hand. Right now I'm jumping around between cells, so every time I look for my place I have to put down a new urge to institute a System. :)
...I actually broke down and wrote the tiddler to generate the table, and one single data-containing tiddler, just to scratch the itch, and went back to trying to maintain my discipline until the job is done.
Tables are an annoyance in any Markdown environment, but TiddlyWiki is devilish in that you know you could write something on top of it to generate the table you're making, and organize the data while you're at it...