I also have used ElasticTabstops for editing CSV files as well as the table editing features of SmartMarkdown &, especially, TableEditor for creating plain text tables in Pandoc-flavoured Markdown. I've wondered whether it would be possible to add more "spreadsheet" type features. (The tables I use are text without requirements for formulas.)
If any Python hacker out there is looking for a project I would very much like two features:
Sorting. Sort by columns. Limit sort to a specific table (in the case of Markdown).
Filters. Fold all lines matching (or not matching) a regex. The ability to limit by columns would extra-awesome.