I know you've already gotten responses to this request and have written an update already. I just wanted to let you know I disagree with the statement that "Baby showers are just for first babies." Some families my agree to doing things that way because of their traditions or beliefs, however, there are other families out there that DO celebrate every new life being brought into this world. What better way of doing that then with your friends and family? I took a moment and searched for the correct etiquette of more then one baby shower and this is what I came up with...
Showers for second (or more) babies
Q. Is it improper to have a baby shower for your second baby, especially if the sex is different?
A. It is never improper to have a baby shower. A shower is so much more than gifts. It is an opportunity to gather family and friends together to celebrate the beginning of a new life. The birth of a baby is a joyous occasion, and it is always acceptable to celebrate it. If other family members or friends are concerned about it being improper to have a baby shower for a second (or more) child, there are ways to take the focus off the gifts. If the second child is a different sex than the first, it would be fun to host a "It's a Girl" or "It's a Boy" party, where guests bring gender specific gifts. Or, if the mom-to-be truly does not need anything for the new baby, forego gifts altogether and just gather to celebrate. Another option is to host a casserole shower or a pampering mom shower.
source: http://www.storknet.com/cubbies/babyshowers/etiquette.htm#4
You see, it's not about the "gifts" as many may put it, again, it's a celebration. Every baby is special. I had this same situation occur during my second pregnancy. I didn't care if friends or family came baring gifts or not, just the fact that they came to share in my joyous time meant something. A friend gave me a hard time in the whole situation. I told her my mom was hosting this for me and if she didn't deem it appropriate, she didn't have to come, and in the long run she didn't. My family throws a shower for every baby being born! To some people it's a sentimental part of pregnancy and life. Not to mention things are changing all the time with each passing generation. Things that weren't considered good etiquette back many many years ago may not be that far fetched anymore. Enjoy your time with your friends and family and celebrate the new life you all are welcoming! Good Luck!