Well, in answer to your questions -getting a bit calmer and staying home a lot more is both a natural progression of motherhood AND of getting older! Even if I were still single or child-free, I could not sustain the party schedule that I used to keep! I was quite the free-wheeling hippy chick myself, and I had a fantastic time. I've just found though, with getting older (I'm 40 now with a 2 and a 4 year old) that I'm not as interested in going out 2-4 times a week any more. I had kind of reached that point when I had my first. I DO still go out once a week either with friends or my husband. We do a variety of things -but one of our main interests is going to see live music. We still love the bands and music we used to go see, so we haven't stopped. We also still go to music festivals and camp -but we take our kids. SO -that's a big change compared to the 4 day weekend romps we used to go on!
Social life can return now! Find a few good sitters in your area. Use Care.com or sittercity.com if you don't have some good references for some right now. Save up your money and try to go out at least twice a month. Even if you only go to a cheap dinner or have some beers at a bar, you'll feel like you've gotten out and taken a break. Look up live music and save up for some tickets -go see a band and dance and have fun together! I know it depends on your finances as to how much you can do this, but I'll bet you can get out more than twice a year. And yes, from what I hear it gets easier and easier the older your kids get.
Have you met any friends in your area? Ever go to any playgroups or other mother groups? I found several women like myself who love to go out through our local neighborhood playgroup system. We often get together for wine nights or to go see bands. Our husbands have become friends too, so there's a wider opportunity for socializing.
Just remember -no matter what you do -your kids are still going to wake up at their regular time the next morning! That's probably been the biggest change for us when we go out -you don't STAY out very late (midnight is usually my cut off) and you really watch how much you drink. As you referenced -it's NO fun being up at 6:30 am after 4 hours of sleep with a wicked hangover and two little ones! It took one night of not thinking to cure me of that forever. Start going out as often as you can though -dinner and a movie may sound boring, but it's actually a lot of fun! You can still let your hair down and dance, so make it your resolution for 2011 to find more of that to do. See if there are any music festivals or day festivals where you could take the kids. My kids love seeing us get down and jam to good music -and they love dancing to it themselves!