I’m not sure what the best breakdown is. On the one hand, repeat visitors are good because they keep coming back and might help spread the word about your site.
On the other hand, new visitors from search engines and referrals are probably more likely to click on your links and sign up, whereas your repeat visitors probably already have an account at whatever casino(s) you promote.
I guess it boils down to what your goal is – visitor loyalty or lots of new signups? Of course everybody wants lots of money now, but I believe that the former can help you achieve the latter if you are patient.