it is the question that you need to ask yourself that how much revenue you are generating through your website. if you are getting targeted visitors than you don't need to do marketing.....
25k hits is nothing! you want get more uniques. 25k unqiues is very good. go ahead with advertising if you are confident you will pull that money back with ROI (Return of Investment)
hehe I wouldn't have put it quite like that, but it's close. Does the question even have to be asked?
Good if you got such a good traffic but to grow a business you need to invest a little profit in advertising.