The RSPCA is important. It's competently run, certainly by the standards of other charities, with a clear plan on how to make life less crappy for animals mistreated by people.
I think I agree with Resident - being obligated to publish detailed accounts probably would kill off some of the inefficiency in the sector.
They are not corporate businesses. The hint is in the name "charity", they are literally not corporations. They're seriously restricted on how they can spend money (it has to be inline with their objects, roughly analogous to a constitution). They do need to raise money, and are somewhat limited in how they do so, but this is solely in order to further their objects. For the RSPCA, these are along the lines of better treatment of animals.
I'm completely indifferent about the "wealth screening" stuff and irritated by the ICO fining them, probably because I consider the RSPCA to have the moral high ground over the ICO.