Personally I think too many places place priority on getting a high number of strains. I think that just confuses people. I think 9-12 is good, with those being a nice mix of indica, sativa, hybrid and also a price range mix too. At least bargain basement strain.
Give me 10 or 12 strains that I WILL want to smoke over 30 strains with half of them not worth my time. There are places I feel totally overwhelmed and if I know there are several people waiting to come into the dispensary I tend to feel rushed.

I am still looking for my "come to Jesus" strain. Since I am heading up to THC tomorrow I hope to come closer to my goal.