Well, a few years in age difference could make a big difference. For example, I have a friend. She was the oldest of two kids. She was 5 years and ten months when her little sister was born, and she says that they were never very close, because their ages were so far apart.
I had my second when my first was 2 years and ten months. And my two oldest are very close, and usually get along great. I had my third when my second was 1 year and 3 months. They are a boy and a girl, and have different interests, so they are not as close as my second and first, but they do seem to be close, since they are close in age.
My next kids (twins) were born when my 3rd was exactly the same age as my first was when I had my second. They are not very close, but I think it is because the twins are very close. When I had my 6th, the twins were the same age as my 1st and 2nd, and my 3rd and 4th/5th. When our newest addition arrives, my youngest will have just turned two.
Hope this helps, and Good Luck with your next baby!