This is the main reason I cancelled Prime. They started advertising "More than just free shipping", and I realized that I only used it for free shipping, and as Prime got more and more expensive I wasn't getting any value from it.
Now I just put stuff in my cart until I have $35 worth of stuff, and get free shipping anyway. It's not that much slower. An extra day or two usually, and it doesn't bother me one bit. I can wait a little while for my $10 guitar strap and it's not the end of the world.