re: Is it worth accelerating mortgage payment to avoid PMI?

Incorrect. Automatic PMI cancellation at 78% LTV is based on the original value, not purchase price. Typically, most banks require you to carry the PMI for 2 years and then auto cancellation kicks in, if you had equity from the beginning aka got a great a appraisal.

If your home appraised for the purchase price, after 2 years of PMI, you can request the PMI to be removed based on a new appraisal. This could be due to accelerated pay or renovations for higher value that would put your LTV to 80% or better.