I have a complete m4/3 system, to go along with a Canon 5D Mark II and a pair of 1D Mark IV cameras. I use the m4/3 for travel, personal work, and as a walk-around camera. With careful technique, a 16x24 inch print looks very good, and a great 13x19 is easy. (By that I mean using a tripod, careful focusing, etc. - exactly the same careful technique required with any camera.)
Right now we have a GF1, a G1, and a GH2, along with the 14-45, 14-42, 45-200 zooms, and the 14, 20, and 45/1.8 prime lenses. The GF1 and G1 share the same sensor, which is fine at lower ISO values, while the GH2 is a newer and better 16-mp sensor. The 14-45 is quite nice, and is much better in all ways than the 14-42 for still photography. However, the prime lenses - especially the Panny 20/1.7 and the Olympus 45/1.8 - are just simply excellent.
To create a lightweight system that covers the focal lengths you want, I would buy a Panasonic G3 or GH2, or the new Olympus OM-D, and the Panasonic 7-14, and either the 14-45 or the 20 and 45 primes. Which lenses depend on whether you will want to shoot street or portrait or photo-j with them, or just lock it down on a tripod for landscapes. My next purchase is the 7-14 (though I'm pretty sure it won't take filters on the front, which might lead you to the Oly 9-18.) Which camera you want depends entirely on taste - all of them have a built-in EVF, while the Oly has in-body stabilization. I've grown so used to the Panasonic user interface that I would just keep buying those, but of course YMMV.
Good luck. Shooting with the small cameras is fun.