Gee, let's think about what a WikiSpreadSheet would include:
There would certainly be formulas, but there are not alot of ways to select things in a wiki.
Internal Links External Links
Words (by index)
Paragraphs could be numbered
Lists could be referenced
Strings could be used as delimiters (e.g. between strings "bla" and string "ha")
Tallys
Basically, we need something like the "class" or "id" attributes for HTML so that we can write a Cascading SpreadSheet??
Whatever.
The next problem is formulas. I suppose something like XSLT would make sense -- but I fear allowing too much power. An executable subset of XSLT without ability to tie up my server or DoS? other people would be nice.