If you're looking at the 5D just keep your current set up. It has lower resolution than the D3100, plus an annoying noise at low ISO which made me when I had to clean up pics from another photographer for a client. The only place the 5D beats the D3100 is high ISO but the 3100 has more MP (though I'm not sure which one has the higher visible resolution which comes down to how strong each AA filter is....but if anything the D3100 likely still comes out ahead). You probably get a little more noise in the shadows with your current camera even though you have slightly more dynamic range, though I'm not sure since I don't have much experience with the D3100 or 5D so these are mostly general observations from that brief 5D experience and doing a few min research. Also they make GREAT crop ultra wide angle lenses, just they're not from Nikon/Canon, Tokina is known for this and used copies are right in your price range. The used crop market is also good right now since a lot of people are moving up to FF so more supply/less demand. I'll ask you about how you shoot in a second but my advice would be to keep your current camera with a new lens, and if you hit limitations there the D3200, 5200, and 7100 all have a sensor with better dynamic range (2+ stops), each step you move up gets you a few features (and slight image quality increase with the D7100) but with landscapes you don't really need much in the way of....well anything, basic AF is fine, FPS doesn't matter, really just a good sensor and that's it. And if you're using a kit lens now you'll get a huge image quality increase with the new lens, so right now what are you shooting with? And when you use it do you find yourself wishing it went wider? Went higher on the telephoto end? Or the range is about right?