It's a touchy situation all around.
While most pleasure boats are too small to qualify for the actual "you're responsible for your wake" rule, it doesn't exempt them from their responsibility to operate their boat in a safe mannner as to avoid the potential for injury or damage to others, and to take in to account the presence of other boats when determining what is a safe speed.
The responsibility to operate your vessel safely exists whether or not there is a no wake sign.
Although there are exceptiions, I think many no wake zones exist to protect the shoreline or environment rather than boats or egos anyway.
Docking your boat in a place with no protection that is exposed to a well traveled waterway is risky at best. If you aren't able to get it in a wide enough slip to avoid it bouncing off of things, or object to the bouncing, then you probably made the wrong choice for a marina.
Personally, I boat for pleasure, am not usually in a big rush, and generally don't mind slowing down to avoid swamping anchored boats, docked boats, people fishing, etc.. My feeling is that as long as everyone is having fun, following the few rules that exist, and not creating a dangerous situation, then the best course of action is courtesy.
The same goes for the owners of the docked boats. They should be courteous too, and accept the fact that the river and it's traffic were there long before they decided to dock their boats in that marina, and they should have known what they were getting in to.