We found that once we had our babies, time spent with friends was a thing of the past. So we say, go ahead, have some fun! Unless there's a significant age difference between your two children, forgo registering and make the event more about reconnecting with friends and family and less about gifts. You'll be showered with those no matter what.
From us : The way we see it, every baby should be celebrated... and who wants to pass up an opportunity to get together with friends and loved ones? That doesn't mean they have to shower you with gifts, though. If it makes you feel better, you can even write "no presents" on the invitations. And why not make the celebration a twist on the traditional shower? Since you've already got one baby, make it a family affair and invite everyone's spouse and kids. You don't even need to call it a shower! These days, some moms are calling the celebration for their second baby a "sprinkle." Cute.