It really boils down to what u use your camera for. Events, official work, high speed AF. You need a dslr.
Family outings, chill out with friends, blogging, street. Then Nex is the solution (along with many other m43 and PnS out there).
If you have a collection of lenses from any brand, u can easily get an adapter to fit them to the Nex.
At this point, nex3/5 is pretty affordable. The c3 is quite pricey IMHO. No harm waiting it out for the nex7 and see what it has to offer before dumping your cash in. But from what I can see, the 7 will be very very deep in A580/A55 territory.

Discontinued, but many shops still have stock.