I'm American, so it's possible I don't understand the purpose of royal patronage duties. But it seems to me that the whole point is to call attention to the charity, for the purpose of fundraising. I might add that I think this is a very worthy "job" and one which the royals are uniquely qualified to do. A private visit from a patron would be a lovely thing for the few people involved, and I hope they all do it from time to time. But as a fundraiser, it wouldn't be very effective.
As I said above, I have been a huge fan of the Duchess since I first learned about her right before the engagement. HUGE. I'm one of those people who stayed up all night long to watch the wedding, which was at 4:00 a.m. my time. I've followed her every appearance. Almost every day as I'm googling for news, I google her. She hasn't put a foot wrong in 3 1/2 years (except for her puzzling refusal to wear underwear in public).
So it's with disappointment that I say that it's beginning to seem that she's more a pampered housewife than a working royal. I don't begrudge the royals their lavish lifestyle, because most of them seem to work hard at a job only they can do. But if I were a UK taxpayer, I would be getting a little upset about the Duchess' obvious enjoyment of the "lavish" part of the bargain, while having little apparent interest in the "work" part.