Actions speak louder than words.
Why celebrate the idea when we can celebrate the already delivered result.
I take your side we don't need the day the idea was birthed. We already celebrate the day the transaction was made. If we celebrate the ideas, then there will be too many celebrations that are not worth it. We celebrate the results and not the idea.
@OP, having a duplicate celebration just for one purpose is not really necessary. The important thing to note is that Pizza Day is being celebrated, and Laszlo is, at the same time, acknowledged every year for coming up with such an idea and executing it.
Se line of thought I had. Totally not necessary without any tangible purpose.