All those reservation fees are annoying, but I haven't found a way around them for individual high-traffic sites. I assume you don't pay that fee if you buy the ticket on site, but waiting till you arrive in the city will probably mean finding at least some things you want to see sold out, plus you'd have to spend precious vacation time buying the tickets in person.
Are you aware of the five-day Passe Partout ticket? It's just 38 euros (apparently no booking fee, even for the Uffizi, but I could be wrong about that) and covers one visit to each of these museums and sights: Uffizi, Pitti Palace (which has many museums), Boboli Gardens, National Archaeological Museum and Museum of the Opificio delle Pietre Dure. If you want to go to the Uffizi and even a few of the others, the Passe Partout ticket will save money.
For folks really gung-ho about museums, joining the Friends of the Uffizi (Amici degli Uffizi) could be worthwhile. For 70 euros you get a calendar-year (unfortunately) membership that appears to cover an unlimited number of visits to the same places as the Passe Partout. That's a lot of money, but I like the idea of returning to a place I loved the first time as well as being able to spread the museums over more than five days if I want to. The Uffizi isn't very large, but by all accounts the Pitti is very time-consuming.