You get, a bigger chip which gives you a faster camera (more light sensitive) and detail. It holds 4 cards over 2 so there is less need for swapping. The lens is more powerful and you can rent even bigger if you need them. You can put more professional controls for the lens on the 500 (to use on a jib or steadicam) You can shade the camera with a CCU.
Do these things matter to you, if they do, it is worth it. The question is can the camera make $15K for you quickly, day rate for a 200 is about $350 a day vs a 500 at about $600 a day. Will it get you more work?
Only you can answer those questions.
All DVCProHD is 920×720 or 1280×1080, unless you go up to the really highend this is true. You can get the specs from the Panasonic website.