Worth or not you will have to answer for yourself.
Each system has their pros & cons, there is no one system which is able to satisfy all your needs. Do weigh the advantages from the 2 cams & decide for yourself. You may also want to rent a D300 and give it a test run to see if you like it.
Comparing the A200 to a D300 is a bit odd. The A200 is an entry level model, like the D40, D40X and D60. The D300 is miles different!! Then again, so is the A700. I suggest you give the A700 a try too, it's a massive step up from the A200, uses the same sensor as the D300 and is a lot cheaper.