I don't disagree with the fact that all babies should be celebrated...but to have showers or sprinkles (cute name, by the way!) for a 2nd/3rd/4th pregnancy really seems like a request for gifts. There are exceptions - like for people that have remarried and it's the first child for their new spouse; they have an unexpected pregnancy later in life (after they've given up all their baby stuff). If you do go ahead with a sprinkle, keep it to just family and close friends or friends that weren't invited to your first.
Most people will bring/send gifts after you have the baby, so why not just leave it at that - or have a meet the baby party. (Which that's just having a get together and saying that it will give people a chance to meet the baby...)
If it's not about the gifts, invite those close to you and specify 'no gifts' and really make it about the company! You can scrapbook pages to a baby album for the new baby (put together packages of milestones and everyone takes one and works on it while chatting, leaving space for pictures that you can add later - they can also write a message to baby on their page and sign it); you can get paints and everyone can decorate bibs - just celebrate the upcoming arrival and have a good time; get a memory or advice book for everyone to share...I think you get the idea!
It's very exciting news to be expecting a new baby! Congratulations!!