There has been alot of "rumors" and project cars that would somewhat represent what you might see for the future 430. I highly doubt the 430 will give you 405hp with only a 10k increase on overall MSRP.
Why lexus would wait till 06? I dont know, I bought my IS new in 02, and even then there was rumors of a 430. BMW will most likely introduce their New M3 in 2005, and I hate to say it, but thinking about going for one of those depending on the body design for the 05 which to me will be a risky considering I'm not a big fan of the new BMW look.
The M3 MSRP's at 45k, so if Lexus is considering keeping the IS300 model and giving options of an IS430, then I would assume at least a 45k tag price with guessing no more then 350hp's.
Nonetheless, I'm really hoping it is released in 05, as someone else already mentioned, its really lacking, and to release in 06 would be a not so good option. The competition in this category is already far ahead of the IS300. They need to make their move soon.
I really hope this rumor of an OPTION IS430 rather then a total REPLACE of the current IS300 kinda worries me. I'm not looking to spend money on a upgraded version of the current IS300, I want an IS430 that is completely new from the ground up, no updated versions of the current model.