The manual will be available for the 2002 model year. It will almost certainly offer better performance (estimate 0-60 around 6.6) , better gas mileage, and better control of the car. The autotrans is basically the same as in the GS400 so it should be able to handle a 300hp "upgrade", but I am uncertain how much "extra capacity" the manual will be able to handle. The current version (e-shift auto) will be alot easier to drive in heavy stop and go traffic or on hilly streets with lots of stop signs (e.g. San Francisco)
Pricing for next year is undetermined. Rumor s of a slight price increase have been heard, but they may not be true. My guess is that the prices will not be much more than they are now, and you may have more room to bargain with the dealers. On the other hand, the people who are getting cars now are getting something "different". By late next year the IS300 will be alot more "well known" on the road.