I used to have second systems in bedroom, used purely as experimental for determining direction of main system. This is where i first discovered SET amplification, single source and/or high efficiency speakers.
I have enough equipment in reserve to add a second system, but no interest since I'd only be disappointed in sound quality relative to main system. I want to spend all my reserved time space for listening hearing the best sound quality available to me. I do listen to a cheapy system at work, often entertain thought of upgrading but ultimately really don't care, listening is only background there, a good system may distract and affect work quality.