The price and details seem pretty reasonable to me. Fundraising to improve the place and reduce burdens on residents dealing with but not profiting from tourism seems smart.
I visited Venice almost 20 years ago, and it was fairly miserable while the daytrippers were there tromping over bridges, but improved dramatically in the evenings and early mornings. I was a backpacker on the road for a year with a constrained budget, but would've been fine with paying $10 had we not stayed overnight.
Flat-out limiting numbers would be a greater restraint, I think. There are a number of places (many in the USA) where visitation is via limited permit - things like climbing Half Dome or visiting The Wave, now climbing Angel's Landing. Even driving through the main roads of Glacier NP or Yosemite NP.