Despite being as different as chalk and cheese, my DDs do play together, they chat, they do each others hair.
They lookout for each other in our large garden, if one falls of the swing etc. the other comes and finds me. I'm happier if they cycle, or go to the shop together as a pair.
As I say they are not alike, if we didn't live in the middle of nowhere, they prefer the company of friends, but as it is they make a unexpectedly good team.
I'm not particularly good at small children, so I was delighted to let them play together or chatter in the car and not have to entertain them.
Yes it's more expensive, and yes I end up taxi driving in opporsite directions, but on the whole I think we all win on the deal.
Most of all having two so different makes you stress less about their faults and moderate your praise. Having two takes on everything makes you a much less neurotic, stressy parent.
It's very rare they both choose to worry me or wind me up at the same time. Unlike DSIS and me they don't fight.
Partly I'd like to say because of good parenting, fighting and point scoring is forbidden and each is given plenty of space and time alone, but mostly luck.
DD1 is dizzy, dyslexic and socially immature and her younger sister the exact opporsite. This compresses the age gap and means sometimes DD2 is better at things than DD1. DD1 has a quiet confidence and doesn't worry that DD2 reads better than she does. DD2 acknowledges, that for all the surface dizziness and hopelessness at making friends, in a real emergency DD1 won't panic.
It's hard to explain, briefly, but somehow they compliment each other in a way that works.