A privateer entering a WRC event has something like maximum 10x10m space for service, while manufacturer teams claim a space big enough to build a factory on... Of course it's a difficult question, as teams claim they need space to invite their guests, and without those guests there wouldn't be any rally either (something many people tend to forget).

But what Mirek said is a very good point. Letting all cars drive on normal (98-100 octane) fuel would make it cheaper. Giving the cars a bigger restrictor to give the "lost power" back (or even a bit more) would be good...
Making a short calculation, for example for Sardinia:
365km SS x (let's say) 65l/100km (or can anyone correct on what a modern WRC car's fuel consumption is?)
1050km RS x (let's say) 20l/100km
Would make a fuel consumption of +- 450 liters. With current fuel price, 5,5 euro/l for WRC fuel, against something like 1,6 euro/l for commercial fuel in most countries, it would make a difference of +-1750 euros for an event like Sardinia, which is probably close to the average WRC event in terms of length. For a team of 2 cars this would save already roughly 50 000 euros/season, without even calculating shakedown and the countless testing kilometers.

Most important is that this would save a lot of money for smaller teams and local drivers, because that's what we are missing most in WRC events. Last year I was in Sweden, I think there was one (1!) Swedish driver entering, is this normal?! FIA should not only look after the big manufacturer teams, but should work on making the sport more attractive and affordable on a lower level too, by lowering entry fees in WRC events for example. If they want to, they can do this for sure.