If you're tight on budget can go for the E-30. There's not many to choose from if you're intending to stick to 4/3 as of now, E-620, E-30, E-5 or possibly a second hand E-3. Alternatively getting lenses of a different focal length range may be what you need? UWA?
The E-620's a good camera, definitely an improvement over your E-520, but personally, no point upgrading to another entry level camera. It's a minor point but do consider batteries as well, of the 4/3 series of cameras, only the E-400+/E-620 series are powered by BLS-1. BLM-1s from your E-520 are compatible with E-30, E-3 and E-5, so you will have your spare batteries already.
Do take a look at elgkh's flickr, he's also a E-520 user and i get inspired by him time after time. But ditto his post, choose what's right for you, there're several bodies that's currently looking really fine as well, the Pentax K-5/K-r, Nikon D7000 etc. So ultimately, choose the camera that suits you.