I thnk it all depends on the actor, of course. From the ones I know of (so far), Mr. Clooney seems to be a fine filmmaker. As in, he makes good movies
overall ... and not just bound-to-be-popular
George Clooney movies, with nothing to sell them beyond simply that. Penn's take on filmmaking is likely
very suitable to good cinema. I tend to think that both those guys, as an example, really love the craft of movies. Ergo, they won't get bogged down in ego/self-promotion at the expense of a well put-together film.
I always think that
some actors who produce sully up the whole business for others who follow them. Notably, say, Barbra Streisand and that mostly horrid "A Star Is Born" remake. I can't remember just now the exact number, but I believe one could count on
one hand the number of minutes she did not appear onscreen in it, in total. It was, more than anything else, "The Barbra Streisand Show"

. And could have been much better without SO much of her constantly.
BUT she's since improved dramatically behind-the-camera. So maybe it's all really a matter of trial-and-error? Even for the most talented and/or powerful of them? After all, an actor looks to get a good part that will bolster his bank account, jack up his popularity, test his skills. A producer, though, has to worry about financing the thing, selling it to get studio backing, money/profit and advertising, etc. Very different ballgames there. A person would have to be mighty driven to do both things (the creative parts AND the 'business' parts) right. Doing both right
at once must be daunting indeed!