how much, on average, do arrow wraps add to the weight of an arrow. Simply, are they going to slow down the arrow at all?

Not enough to make a difference.

True dat.

The 4'' blazer wraps weigh about 5-6 grains, could be a 2 fps loss (I never tested it).
However, if you want to keep FOC as high as it was before you will have to add weight to the tip as well.(Yes, I'm detail oriented)