Manjaro isn't really useful if you already run Arch with no problems. If there's a specific feature it has, like the graphical pacman frontend, then you can always just install that on normal Arch Linux.
I would agree with you, however the time you and I spent installing it was significant. You know me and I'm far from an average user, but if/when I need to reinstall this on another or new machine, it involves quite a bit of dicking around.
Arch is great if you truly want a minimalist OS and for me so far it has been just fine.
However I'm that "middle of the road" professional user. I want a nice, quick, GUI-based install with most of the basic packages I need from the start, then build from there. I don't want to have to spend an hour just getting a core OS installed. Manjaro seems to have that balance that I like. No bloat, just the good bits and since its based on Arch, it has very solid foundations, which I also like.
I installed a test system at work and quite enjoy it. You've already converted me to Arch Ampera, let me have this little thing ;-)