I just had another thought...my two eldest brothers are 23 months apart and my eldest brother was very jealous when my second eldest brother was born. They have a big rivalry between them and though they played together as kids they haven't really gotten along since teenagers.
So having two different gendered kids close is probably good...my third brother & I never were very competitive as we were good at different things. We didn't hang out much as teens but have lived together as adults (to help each other out) and we talk a lot more than we do with our other siblings. We also have a lot in common as adults too.
If your DD is very girly your DS will probably be ok with that when he's young, when they're older there's plenty of games were your DD can be girly but your DS doesn't have to - ie. Dress ups or imaginative games. My brother managed to turn 'school', 'shops' and 'mothers & fathers etc' into non-girly games too.
Sent from my GT-I9305 using The Bub Hub mobile app