While I always assumed I would have 2 kids, after #1, I, too, was not emotionally ready to have a second for a long time. I struggled with parenting, though I wasn't a bad mom--I just didn't know what I was doing (I lost my mom when I was 15, so I had no one to really go to for that "mom" guidance that I needed). I struggled to make routines. I struggled with mom-guilt (I was working full-time at the time). I just couldn't wrap my head around adding another one to the family. When my son was 5, I realized that the thought of another one didn't mortify me anymore. Which was my sign that I was okay with giving it a try. Two weeks before my son's 6th birthday, we had a little girl and I became a SAHM.
Now, they're not going to have the same closeness that my sister and I now have (we're 2 years apart), but he is the most protective, doting big brother ever! A little background: My sister and I hated each other for the better part of our childhood because we were too close to each other (2 years apart, shared a room, etc., we had to share everything--and got very sick of each other very quickly). As adults, we are obnoxiously close, but it took getting to college for that to happen! Given my experiences, I never saw any real pros to the need to have kids super close together.
However, my son adores his baby sister. He's helpful, can watch her while I run to the bathroom, can give her some Cheerios if she runs out and I have my hands full with other things. He's really enjoyed getting to know his old baby toys again and showing her how they work. So, it's a different kind of toy sharing than kids that are closer in age. It's a MUCH nicer toy sharing, in my opinion! And she loves him back. Her face lights up when her big brother gets in the car after school. She giggles whenever he comes near her. And I think that as she gets older, he is going to be the best, protective big brother.
Plus, I don't have to deal with changing 2 sets of diapers, keeping a close eye on both kids at the same time, etc. I know that if my boy is in the house, he's fine. He can get his own breakfast, watch TV quietly, read a book, play a video game--all without my constant supervision. So, I can therefore catch a break once in a while if the baby is sleeping or playing in the playyard.
I've heard that having 2 kids further apart almost makes two only children. Rather, I think it's the best of both worlds. While your son got alone time with you for the first 7-8 years of his life, now while he's in school, a new baby would get the same kind of attention. Then, when the family is together, each gets to learn to share time and attention, which I think is very important in maturing into sympathetic and empathetic kids/adults.
My mom and her brother, cousin and her brother and other cousin and her brother are all 13+ years different in age. They are/were all very close to their siblings in part because there was a more caretaker closeness--more maternal to the babies. I don't think that's a bad thing!
When it comes to you changing your mind on possibly now wanting that second child...it doesn't matter what you've told other people or the identity that you've created. If your heart is wanting another one, that's your decision. Let everyone else be shocked!