10-20 seems like a lot of coins, but I guess it would depend on the size of your portfolio. I can make a case for it or against it, but in the end I would still limit myself to staying below 10. The main reason is that I would rather concentrate on having a stronger portfolio over additional chances for small profits here and there. When Bitcoin drops, no one wants to hold a bunch of crap coins. I am not saying that you are, but often with big spreads that is the case.