...Would there be much difference getting from the same landscape picture taken from two different cameras (4/3 and 3/2)?...
Not having had experience with the E-510 (my last Olympus SLR was an OM-2) I'll leave those questions for others.
There isn't a simple answer to the question of 4/3rds vs. 3/2ths (
) for landscape work. If most of your preferred landscape compositions are a lot wider than tall (or, indeed, taller than wide) then 3/2 might be better. The reason I say this is that while you can frame the longest dimension of the subject with a zoom lens equally well with both types of camera when you come to print (or save the finished article on the computer) you will end up cropping more of your picture away with a 4/3rds camera. This isn't a deal breaker, however, as long as your final print/display size isn't limited by the camera sensor's resolution.
So, in summary, unless you print or display your pictures at sizes where sensor resolution might be an issue there is no reason not to choose a 4/3rds camera. If a lot of your shots look better framed near a 4:3 aspect ratio rather than a 3:2 aspect ratio then there is every reason to go for a 4/3rds camera. It's down to your preferred style and needs.
As always, it is important to try and get down to your local store and see how your short-listed cameras feel in hand. In my opinion that should be your first criteria for choosing a camera rather than worrying about the aspect ratio of the sensor.