I did not feel ready to have a second child, but like you, knew we wanted one and so we just went ahead and did it! ;) It was scary! I think most moms probably feel like you. It's hard to mix up perfection, right?! ;) Anyway, my kids are 2 years and I week apart. I really didn't mean to have them with their birthdays so close, I was hoping for a month or two, but oh well!
I think there are pros and cons to each age difference. There are many times where I want to bang my head against the wall b/c my kids are nuts and are often both in some sort of "stage", but then again, they play together so well, love each other so much and still generally have the same basic interests so it's easy to travel and entertain them with the same things.
My brother and I are 5 years apart and we did not really share much of our childhood. Of course we have similar memories, but really he was a lot older than me and being different sexes we had different interests, etc. BUT, I know my mom was happy that he was older and more independent by the time I came along. Plus, he was out of high school when I started and would have been out of college before I started too (he didn't finish so he was out a lot sooner!!), which is a major help in the pocket book department.
So I guess you have to do what you think is right. Whatever works for you is right but I warn you, you may never feel ready! ;)