I think you answered your own question when you said the extra $200 is not a big deal to you. Here's why:
1) As you mentioned, if you use your 360 for movies and games and either the drive or the 360 fails, you won't be able to watch HD-DVD's at all. Of course, if it's just the HD-DVD drive that fails, you could still play games but if the 360 fails, you're out of both until your 360 is repaired/replaced. Also, if you plan on doing a lot of movie watching, you're putting more wear and tear on your 360 (would could be important if you don't have an extended warranty).
2) The 360 HD-DVD will not have HDMI nor will it have the ability to output TrueHD au dio. Without HDMI, you won't have the ability to upscale SD-DVD's and with only an optical audio output, you won't have TrueHD. These might not be big issues to you, but it does make the extra $200 seem worth it IMO.
NOTE: As others have mentioned, the 360 isn't out yet so we really don't know how it's going to perform. Will it be faster than standalone units? What audio formats will it be able to output? Will the PQ be as good as the standalone players?
Now then, I can see a couple of reasons why the 360 drive might be a better choice:
1) Not confirmed, but I assume you'd still have access to your 360 Guide during HD-DVD playback. This means you could still check your friends list and receive incoming message from your gaming friends. So you could feasibly watch an HD-DVD while waiting for a friend to page you when he is ready to play a game (for example). Again, I can't confirm if you can do that but it would seem logical that you can since it works when you play standard DVD's.
2) The 360 HD-DVD drive seems to offer a great value at $200 with a free movie and remote. If you are a bit nervous about jumping into HD-DVD because of the format war, then it's a relatively inexpensive way to get a player and see how you like it. And again, the 360 drive could be faster than the standalone units which can take quite some time (G1 players for sure) to boot up and play a disc.
All that said, I already have an HD-A1 standalone player but I'm thinking about getting the 360 drive as well! I think it would be nice to have both, but my recommendation for which one you get it ambiguous. Since you mentioned that the difference in cost is not a big deal, I'd probably say just get the standalone and be happy with the best output options.