the only 2005 changes that i've heard we're confirmed are:

the passenger seat will have 2 power controls in the touring.
the radio will be able to stay on RDS
and supposedly there will be a passenger side glove box under the dash.

Honestly I don't believe these at all.....too many Z owners would be pissed if they changed the car that much....especially if they bumped the horse power.....i don't see that happening due to both the Z loyalty and the release of the Infinity Skyline