I think that's about the only benefit most people see when they trade sideways from Mikrotik or PFSense. Like everything else in the Unifi range, there is nothing special about the actual hardware and nor is the functionality of the units particularly exceptional. USG and USG Pro are perfectly good router/firewall units but the real benefit comes from the "single pane of glass" management that Unifi gives you. If, like me, you have 5 switches and 12 access points then the "one click and you're done" aspect of management make life so easy.
But if you already have something else, there is precious little reason to sidegrade unless you want all the bubbles lit up. If I'm totally honest, that's why I have a USG Pro. I wanted all the bubbles lit up and I wanted it to match everything else in the rack. When the lights on the first batch didn't line up, I waited until the revision came out and put one of those in instead, because I wanted all the lights lined up.
I will say the resale on UBNT is excellent, mainly helped by the strong dollar. Anything bought before the Brexit vote can be sold for effectively no loss in value. So there is an upside to everything.
Absolutely, just looking at the USG (and even the pro) they don't compare on hardware specs to the RB3011. Where the MT stuff is very swiss army knife and will do anything you want if you know how to. I'm pleasantly surprised at how much the USG is doing. There are a couple of bits I need to finish up my "transition" such as 2 VPN tunnels outbound, a PPTP and an L2TP as well as hosting a PPTP server for a single user to dial back in on. Some policy based routing which I'm very uncertain I'll be able to do without going all CLI on it so I'm not convinced of the jump and think I'll probably go back to the trusty old RB. Shame really as I like the Unifi interface and more so as I have a PoE switch thrown into the mix.