I would say since you don't seem to think you're going to sell the notes anytime soon save your money and rather than spending money on having a TPG to look at your notes spend the money on notes you want for your collection!!! Between Shipping and grading the notes the cost can quickly add up. Personally i have been taking some of my notes out of TPG holders only as an exercise to see why the notes got certain grades as AU, Unc, CUnc and GUnc as they all look the same to me in those holders.
Cheers
MG