I am afraid I am one of those English women that thinks baby showers are mostly about money-gift grabbing (ie: people who only want certain items and wouldn't be happy with *any* thoughtful gift), so I decided that if I ever have a baby shower, I will do something like you, try to convey that gifts, whilst appreciated are not necessary and would be capped at around $20- so that if people really do want to purchase something, there is no pressure on price and people can always find something useful- just things like nappies etc for that price, then it doesn't feel "grabby".
I totally share your concerns and it's so nice to see it! My SiL just had her shower and it was so crass about "what will I get, look what I got", it was another reason for me not to go and I did not take any notice of her registry (urgh!), I bought a very cute "take home" outfit from Boots in CREAM! As it happened they were delighted with it.