Greg, I am a long time viewer but first time post for me. I don't want to come across as being bias because I represent a NEW wakeboard tower speaker company; Wet Sounds™. Although, we do not sell our bracket by itself, currently, so I hope that you do not take what I am saying as a method to sway you over to our "trick connect™" concept.
Reading your request on quick release bracket I can tell you that during our research and development phase, which was well over 2 years worth, we were first approaching the concept of quick release. Our first idea was using a pin that just needed to be pulled out when you wanted to take the speakers with you. However, during several months of playing around with different concepts and ideas we encountered one major hurdle. If you use aluminum, which most are, you need to take in account that the dynamics and tolerances of this material changes based on temperature variances. Simply put, when you insert it and then run your boat all day long in the sun; at the end of the day your aluminum pin has expanded thus making it difficult for removing it. Additionally, we also discovered that with using a "pin" concept has lots of movement within where the two brackets meet. That, for us, was not acceptable as it opens a potential for disaster.
On side note, with regarding cost, it is not so much a demand issue on the consumer level as it is more so of commodities and inflation issue. Aluminum had 3 price hikes in the last 6 months and will continue to increase because of the lack of resources to provide for the growing demand. With that said, that bracket you see today for $70 each might increase to $90 by this time next year.
Anyway, I just wanted to share our experience as a company that we have identified on a professional level. With that said, however, still take it as a grain of salt as there are good products out there with good R&D put into them. Good luck. http://www.wetsounds.com