Speakers are just a big box enclosure with a lot of dead air and few speakers in the front."
Not quality speakers, there are actual formula's for proper spacing and porting of speakers for proper sound.
As for a complete plexi-glass enclosure, I wonder if there would be a problem with static from all that plastic? I know that some of the new case mods have a lot of clear plastic, but the panels are mounted to metal. About a month ago, I ran across a web site dedicated to wild case mods. They use the new micro-mini boards to build systems in everything (briefcases, ammo cases, etc.).