I agree there are plenty of big flavors here without the bacon - but if you want to replace its smokey flavor, you could add some smoked paprika (goes well with mushrooms, etc.) or some grated smoked mozzarella along with the parmesan.

a little late to the game here--but i often use sun-dried tomatoes instead of bacon and prosciutto when cooking for vegetarians. they give that savory, chewy bite that i associate with salty pork products!