Given enough horsepower in a machine, a very large buffer just isn't necessary. This was the point of introducing anti-buffer underrun features, so that small buffers could be used without fear of creating a coaster, thus cutting costs. Of course it is nice to have a large, comfy buffer, but it isn't necessary. While Yamaha's P-CAV does offer a bit of a speed improvement, it just isn't astounding. Burning an entire CD, the average speed of the Yamaha is less than 1X faster than the Lite-On. I agree that the Mt. Rainier has a lot of potential, but by the time it has enough support to be worthy, the drive itself will probably be around the Lite-On's current price, and DVD burners will be competing fiercely.
Certainly, I also agree that these features are beneficial nonetheless. I just don't see it as worth the added cost, but that is my opinion. It's obviously different from your's, so there's no point in arguing What's important though is either of these drives will serve their user very well, and Arcenite will be happy regardless of which he chooses.