The turbulence caused by the spoiler will cause internal damage to the flaps if they are extended ANY amount. I do know that it will cause the flap skin rivets to loosen up. As for control effectivness, not a problem. The controls of the Lear 20s and 35/36 are more than effective enough to compensate for the pitch requirements.
After talking with some of the old Lear test pilots, it was not because they were concerned that it would loosen the flaps. It was because it WOULD loosen the flaps.