Your gs500 compared to a GL2 are apples to oranges.........the GS is a consumer formated camera, with manual controls that are not real user freindly......the GL is a pro-sumer model that has decent manual controls and will produce better footage because of this.........picture quality may be very similair, but the footage will be of better quality because of the ease of using the manual controls...........also lowlight will most likely be better with the GL2 as you can open the irirs and slow down the shutter speed, also i believe the GL has a gain feature which will give you more light (but don't go over 6db as it gets very grainy after that) My DVX100 has a gain up to 18db and can shoot in very little light but the picture quality is too grainy to use in any kind of broadcast work.

If the GS500 is what fits your budget then by all means buy it, it will be a good starter camera........but if you can swing a few hundred more go with a GL2 or DVX100b you will be money ahead in the long run