K.-
As I am sure you know there is no "right" answer, but I will tell you a little of my story, which may help.
I had my first daughter directly after high school, my next daughter 11 months and 8 days later....no I would not suggest that CLOSE, but they are now 14 and 13 and best friends, just as they have been growing up. They hit their stages different but the younger of the two caught on faster watching her older sister.
It gets better, years later I remarried and now have added a 4 yr old boy and a 10 month old boy to the mix...yeah, four total.
The older girls are wonderful with their brothers, and even they joke about how wonderful birth control it is having to help or listen to a crying baby at 2 am!
The boys are close, and although we were only planning on having the one, I am glad for my lil' Jack who will be one in June...but honestly, if I had it to do over again, I would have had my boys closer together.
The girls were always busy together and even tho, like all kids, they had their "times", they are each other's best friends and will be for life. The bond they have with their brothers is a little different in that the boys look up to them for help or assistance, but also an automatic playmate! Maybe in a few more years when the girls get more involved with boys they are NOT related to it will be different, but that relationship is solid.
I sometimes feel bad for my baby because he gets left out a little, being a crawler he can't not keep up, no matter how fast he goes! But if I knew he was in my future I would have had him closer to my 4 yr old...
Hope that helps...I think closer is better, but love the bond that I see with my 14 yr old and my 10 month old....
Kim