Some of those artists will then use any boost to their magical powers in the production of their works, others produce art completely by hand and use the royal gift to help with life outside of their art. (Most artists are in debt, extra magical powers can come in handy here when dealing with bailiffs and so on).
The Queen feels her presence at galleries and libraries to support specific events is enough patronage to be going on with and, in any event, if you want patronizing, just listen to Roherum's commentaries on such royal visits. He really does have that down to a fine art form!