I have 3 children, 2 boys and 1 girl. I had my first at 27, almost 28, and had waited a lifetime to be a mom. I had my second, a daughter, when the first was 25 months old, and me almost 30. That was hard. She didn't like to nap during the day, but she slept wonderfully through the night from around 6 weeks of age. It was apparently hard enough that I didn't want another one immediately and, in fact, neither of us even mentioned it really for a couple of years. I used to joke with my husband about a third, to which he would reply "No way!" lol. He wanted a vasectomy, but as time went on, that joking' wasn't so much of a joke any longer. I wasn't dead serious about trying, but if he would've agreed, I would've done it.
When my second was 6 years of age, we were surprised with #3. Number 3 was such a joy in every single way and just seemlessly blended into our family (barring his naptimes falling during sports practice and game times). I have never been so thankful as I was for him -- knowing he was my last, I relished in every single moment we had. Suddenly rocking a fussy baby during my favorite show wasn't an inconvenience, it was treasured, and I more than willingly rocked him to sleep for every single nap and bedtime he had, having to hold him upright due to a stuffy nose wasn't so bad either--suddenly just staring at those rounded cheeks in the dark was wonderful. We still do rock from time to time, at 2.5 years, but he is soo big.
I feel like with your first, you have such a strong desire to do what's best for them, by the book, so to speak, that you almost don't get to enjoy it -- you wind up trying to figure out how to get a shower, get some sleep, cook yourself something to eat, how to feed them right, lay them in bed right, trying ot figure out what every cry means, etc. to where you feel almost frazzled just because of those reasons. I'm an organizational freak and working a baby in threw a glitch into my "flow." Don't get me wrong, hubby and I are the biggest kids ever ourselves and people used to comment how they'd never seen 2 parents enjoy a child so much (with our first), but it was an adjustment nonetheless.
When I had the second, whoo boy. I was now appreciating all of the time I didn't think I had with the first that I was suddenly shown had really been available to me. It was a glaring difference and made me sorry I hadn't appreciated all of that time more with only 1. The upside and most memorable is how much she loved her older brother and how much he loved her (after the first few days home when he couldn't figure out why some habits I had established with him could not occur as usual due to the new baby). She would sit next to him and stare at him all day long if she could. She used to laugh as he took a bite of some food. She adored him. As she grew, they often snuggled each other just because they were close. People used to comment at how cute they were and ask "Do they always do that?" (as they walked in public hand in hand. Now they are 8 and 10, and although they still play well together, they have those miserable-married-couple moments, which will pass.
Even with such a big difference between my second and my third, which is definitely easier as far as communicating with multiple children (2-y/o's aren't that great at it and still require a lot of attention), I could suddenly see how much time I had available to me with only 2 that I took for granted and did not take advantage of. I'm almost 40, and my last is 2.5 years old. I wish I could give my daughter a sister, because I can't imagine life without my 3 sisters - (we fought like cats and dogs through our adolescence, but as mature adults, we have found the best ear to bend whenever we need to,) plus they know why I'm crazy in MY way, and I understand why they are "crazy in THEIR way. I couldn't ask for a bigger feeling of support, and I hope and wish the same for my 3 kids.
As for people asking that question, I think they just get excited about a new baby coming, period. I know that I just LOVE when other people have babies. Maybe they ask because they are so close with their siblings and can't imagine life without them that they think all sibling relationships turn out that way. I think they don't mean to be disrespectful.