A Travel Camera...what to choose?

I am a rookie guy who likes to take photos. At the moment I have a Nikon D3100 which i have travelled with once to Norway, it served me quite well, I didn't always have the right lenses but it was pretty good. I'm going travelling next year for about 7 months to South East Asia, Australia, China and Russia (well thats the plan, we'll see how it goes). Naturally I like to capture these moments, people and places. I see two options:

1. Keep the d3100 and invest in a lens, (17-70 or 18-200?). It will be heavier but offer good performance but be much heavier. Also save money which is always nice.

2. Get a mirrorless camera which seem to offer perfectly good image quality and better video then the d3100 (in terms of ease of use). I have been looking at the Panasonic GX1 and Sony NEX series, they are not a preference just have got good reviews. One problem with this bunch of cameras is the lack of built in viewfinder unless you go up in the price range. I'm used to one with my D3100 and its something I want. The GX1 EVF is £200 which is quite a chunk if you ask me. Next question is which lens to get if I go with one of these? My budget would be up to £800 ($1200, wow the dollar is weak against the pound at the moment).

A lot of questions, thanks for any opinions!