I have an ex. Oh, the stories to tell... They only seem funny once time passes... anyway...
Back to installs, why make work when it's not necessary? Joint compound may well be cheap, but your time isn't worthless. Likewise, go into junction boxes more than a few times... you learn to make it as few as necessary. You're up against all kinds of mistakes, both ones you might make AND the past mistakes of others. It doesn't sound like all that big a deal, and perhaps a lot of times it might not be. But in the few times where it MIGHT be you're risking smoldering fire due to loose connections and arcing.
I've dealt with everything from knob and tube, to cloth/asphalt, to aluminum, to modern Romex (and probably a few others I've forgotten). I've also had the opportunity to revisit some of my own work in the past... and have been less than impressed a few times. Mistakes get made, try to plan well enough ahead to minimize their quantity.
I'm not one to exaggerate or panic. But when it comes to line voltage AC you do not ever want to start thinking about it as 'not a big deal'.
Or not, I'm just offering advice, make of it what you will.
Yes, you can layer hubs through another system. I've got both Ra2 and Caseta connected through Ra2. Why? Because Lutron in their infinite wisdom has decided not to offer an on-wall plug for Ra2. I like Caseta's on-wall gizmo and put the added time and expense into rigging up a Smart Bridge Pro and a HS3 plug-in just to get that. The downside is the only way I can control one from the other is through HS3. Which is fine for this simple setup, but for whole house lighting it'd lose a lot of Lutron's nice scene coordinating. That and by the time you add up the cost of the pieces you're often right back up to Ra2 level.