I've been using the E-520 since about the time that it first came out and the camera has served me well. At the time, I lusted after the 14-54 lens but it really was beyond my means.
However, now that the II version has come out, the original version can be found used for a reasonable price. From what I've read there are no significant differences between the lenses, other than more rounded aperture petals and better autofocus in live view (at least from what I've read). It seems to me this would be a worthwhile upgrade.
However, I'm a bit concerned about investing further in the Olympus 4/3 system as it seems there is a serious lack of cameras currently. The only new body is the E-5. Is it time to think about getting out of the E-system cameras or should I just happily keep clicking away and get some new glass?