If you are getting 5000 visitors with just 3 pages, then why not try to build some more good quality pages so that you can get more visitors and high earnings.
I think there is absolutely no problem in sprinkling some high paying keywords in your articles UNLESS you over stuff the pages too much. A keyword density of aroun 2-3% is OK with google.
I honestly don't think that Google should have a problem with it. Just remember to stick to the rules or else!!! :0)
It is a better idea not to stuff high paying keywords unnecessarily and puttting more unique content can pull more people to your site .Alos find why your site with only 3 pages is so popular and then monetize it .