Patrick, although I've never stayed overnight at the dock, my slip is fairly close nearby and I think I can answer your questions.
First, this is the very best [and expensive] place to stay at Bethel Island as far as public docks/RV parks go. They try to make everything "first class". The No Cancellation policy is because they are in high demand in the summer. However, I'd suggest speaking to the dock manager, different then the RV manager, I believe, to see if he'll refund if someone else rents your space. Get it in writing!
Security is as good as they can make it: locked docks; personnel with their eyes open; cameras and alarms. However, access to the docks from the water is where thieves, who like Sugar Barge as a target, can gain access. Ask your neighbors to keep an eye on your boat and you'll do the same for them. I have a motion sensing device from Radio Shack for $15 that sets off a shrill alarm. Works really well with no false alarms!
Noise from the restaurant can be very loud if they are having entertainment on the outside deck! However, they shut that down after 10PM and most music is in the daytime. Inside the restaurant and bar can be very noisy but they have done a good job of containing it to inside, so the docks remain quiet after 10PM and until 9AM or so. They strictly enforce the rules at the RV park and the docks.
Boat wakes can be a problem and most wakes will hit broadside, but most boaters know that entire end of Piper Slu is a "No Wake Zone". However, they are near the seawall opening so a lot of traffic comes and goes.
They have very well maintained, clean showers which require a combination to access. Again, this is a first rate resort!
Have fun and let us know how your visit was after you return!