Can't say about the fee, as I almost always camp and pay the $10 in the first place.
Mike is the long-haired guy, around 50-ish(?), that lives at the ranch. Not sure if he's owner, manager, caretaker, or what...heard all versions. He's always been nice to me, but there are several who have had problems with him. I don't really know him, other than from occasional visits to the ranch, so I'll stay out of that debate.
As for leaving the springs after sunset, I would recommend caution. I've seen rangers walk right through a large group of nude soakers/hikers without a word about nudity, while giving stern instructions to be leaving the creek area when the sun reached the top of the ridge on the west side. If they wanted to ticket you, it would be hard to defend against it, since you pass a steel sign that says "Day Use Only" if you hike from Bowen Ranch. A lot of folks ignore the rule...use your own judgement.