I have heard conflicting information on this topic myself. I have heard that repeating something too much can damage your reputaion with the engines and possibly get banned, but I have also heard that you need to repeat it enough to be recognized for what your site is about.
I would say that a safe bet would be to just stay informative about your subject of interest. Repeat it a few times in your text, but use variations as well. As with money, you could use bucks, mulah, wealth, etc...
Best of luck to you.