So I am making a cake, chasing my kids, paying attention a little here and a little there. I realize as I am watching my RV rise, I forgot the vanilla. My immediate thought is to infuse a little vanilla through a vanilla flavored simple syrup...what do you think? Will it work? Should I suck it up and re-bake???
Vanilla has an important purpose in baking. It cuts the taste of eggs. That's why you see it in almost every single baked good, even if the cake is supposed to be almond flavored, you will almost always still see vanilla in addition to the almond. Without it, baked goods tend to have a strong eggy flavor.
That said, and without knowing your particular recipe, I would go with your idea of the vanilla spiked simple syrup.
I'm assuming RV is red velvet...Depending on your red velvet recipe, you might not even notice it. The food coloring gives the batter a strange taste and the vanilla isn't usually too noticeable. A syrup mgiht throw the flavor off, actually.
Can you cut a little edge off and taste it to decide if you want to do the syrup? You might not need to.