Or if in case I am not looking to invest into expensive lenses I may as well be better served with advanced compact.
I would agree with that sentiment, so I would recommend a Sony RX100. (Full disclosure: I own one.) Just keep in mind that, when shooting indoors, you'll probably have to leave the lens at its widest setting and "zoom with your feet", as the saying goes. (Also, note that the RX100 has the same size sensor as the Nikon 1 series, so there's no advantage to the Nikon unless you buy other lenses, which you've decided not to do.)
Then, in 3-5 years or so, upgrade to something else (maybe with hybrid contrast/phase detection AF which by then should be much more common*, and likely cheaper than it is now) since you'd probably be looking to upgrade around then anyway, even if you bought a 4/3 camera now.
And lastly, re: "And whether APS-C format advantage in low light is so high." -- as someone who owns both an Olympus E-PL5 and Canon 70D (with an APS-C sensor), I would say no, there's not that much difference between the two camera bodies. As usual, with interchangeable lens systems, it's more about which lenses you use them with. And with comparable lenses mounted, the E-PL5 is much
more portable than the 70D. And since portability is an important criteria to you, I would think that would outweigh only slightly better low-light performance.
*note that your statement: "4/3 format but ... none of them has phase detection" is incorrect, as the Olympus E-M1 has phase detection. Not that you should consider buying an E-M1 now since it's over your budget, but that's why I recommended waiting and upgrading in a few years...