Meta Tags were once a major player in SEO. With the advancement of search engine algorithms, meta tags become less and less significant. The description meta tag is still used for your search engine snippets, but the keywords meta tag has been disregarded by all the major search engines.
The Keywords meta tag is useless, except for misspellings.
If your page has a product, service, or keyword that can be misspelled, instead of intentionally misspelling the word in your text, use your keywords meta tag. It won’t get you page 1 placement necessarily, but it definitely makes a difference.
If I had say in the Googlerithm, I would tie the spelling functions with the search functions, and if a page ranked well for a certain phrase, but the user misspelled the phrase, I would certainly give more relevance to a page that had the misspelling on it (albeit in a keyword meta tag).
With that said, I would certainly not focus much time at all working on the keywords meta tag, but while you’re under the hood making changes to your site, it wouldn’t hurt.