You can promote your site on wikipedia only if it's a really useful resource. Otherwise they will remove your links in no time.
If you are planning on making a page for a particular company it could get removed rather quickly, unless the company is really well known and branded. Yes, the link the give you is nofollow... but the traffic you can get from a Wiki page makes it well worth it to have your link there. I would recommend finding a relevant page that has external links, and creating an article around the exact topic of the page. As long as the article is informative, on topic, and not overly promotional it may stick... at least for a while. From an even modestly popular Wikipedia page you can get some really good traffic. So yes, its worth it regardless of the nofollow.
It's good as long as your link is relevant to the article otherwise, as said repeatedly, it will be deleted sooner or later
I learned this lesson for myself. I put my link in a few wiki's that had to do with what my site had and they were removed within a day.