I have diamond. Is there any difference worth noting between the enhanced adition and this?

For me it's more content. New official modules, more tools for creators and almost all popular servers migrated to EE.

For PC single player not really yet, it's mostly promises of things to come. But you'd need it if you wanted to play Darkness Over Daggerford and Tyrants of the Moonsea in their new Premium module version. I thought the EE on its own is not worth it yet, but these two Premium modules are.