Picking up a new girl is not quite the same as reigniting some old passion in someone you have already "done" so to speak. New girls are always easier, since you will be more interesting to them than to your wife.
You have probably done something wrong in your relationship, killing it slowly. Been there, done that (yes, 10 whole years). I have a new relationship now, and here is how I will keep it alive, in case you want to try it out on your wife:
1. Let her have her hobbies and interests, let her meet other people and have fun on her own. With other words, let her have her own life, and trust her. What I expect is the same in return.
2. Be unpredictable and surprise her! Buy her gifts, make dinner, take her on a trip... Always try to make new things up. This requires some money, but doesn't have to be that expensive. However, children tend to drain your purse quite quickly (especially if you need a new car, new house, new everything at the same time). So if you have toddlers you just have to persist a couple of years. I'm currently in that phase.
That's about it. However, we can add a third point, which is more or less an extension of the previous one:
3. Arouse her! Learn to read her signals, how to respond to them, and do whatever it takes to arouse her. Make her life interesting again.