I do this, but you do need to be kind of explicit.
I sent out a message to everyone explaining that "we don't have space for loads of gifts, some visitors may be worried about money this year, and if some people give gifts while others don't, this will create embarassment. So we do have to ask everyone to please not give gifts, so that everyone can just relax and enjoy the party." I added that if people want to bring a food or drink item to share at the party, they're very welcome, and that there's no need to bring anything expensive. It actually started a trend among my friends, I think, as I have noticed more and more others doing the same over the years,
If you just kind of mumble "Oh, no need to bring presents," most people will still bring one, and those who didn't will be mortified.
But I'd really welcome being told gifts were optional.
God, no! This will create confusion and embarassment left right and center. If you want no gifts, you need to be clear that it's no gifts across the board.
I'm fed up with people sucking the joy out of everything!
The problem is that not everyone has a big house with a loft and all that. I have a modest flat and my office is a corner of the living/dining room. We have to be really careful about accumulating stuff. Clutter makes me feel ill, and it's harder for me to be a happy and patient parent if I'm constantly having to waste my time decluttering and sorting and organizing and throwing away piles and piles of toys and plastic. I've learned from experience that it's better to set boundaries firmly and be a happy parent, rather than put up with things I resent and be a resentful, put-upon parent. My kids have enough toys (trust me), and I also have the right to feel comfortable in my home.