We're one of those couples that chose not to learn the genders of our children before their birth, so people really had to wait until the babies were born to provide gifts if they wanted to do something gender-specific.
I personally didn't want a second baby shower. It's traditionally against etiquette, though it appears the rules are beginning to bend a little. If you'd like the opportunity to get together with these people and celebrate your new baby, I'd not refuse it. If it were me, I'd say that gifts are optional, and that you don't know the gender.
There's nothing wrong with people getting something cute, putting a gift receipt on it and allowing you to exchange when the baby arrives. We found that there were a plethora of gifts after the births of both children to accommodate gender (we have one of each).
As far as gender neutral items - most of the clothing really ended-up not being so cute (4 years ago at least), but we still used it as pajamas, etc. It was nice stuff, but it was so much more fun to dress a little girl in ruffles and a boy in gender specific items as a new mom.
However, there are always things that you need for babies regardless of gender. My standard baby shower gift is a basket with the necessities (even if they've registered elsewhere or gender specific) - bath wash, infant tylenol, lylicon, wash cloths, safety swabs, diaper rash ointment. I make a list of all the items, why I included them and a funny story. For instance if I give petroleum jelly, I might say: "helps keep baby's skin soft, diaper rash away, and controls fly away hairs as a bonus". I put it in a practical bin that they can use for storage or baby items that I may or may not decorate, and I always include a gift receipt for anything they may want to exchange.