And in yeast there has long been evidence for WGD. See, e.g., https://pmc.ncbi.nlm.nih.gov/articles/PMC4529243/ & references therein.

Edit: I posted this without looking at the paper (which is about yeast). Doh.

Gene dose increases in plants lead to bigger vegetables and fruiting bodies. We've taken advantage of this during domestication of several species.

Gene dose increases in animals lead to total dysfunction and death in embryonic development.

In bacteria as well!