You must be just bored because I don't think it's worth it.
Give your '04 a chance to age a little before the upgrade. By the time your literally tired of the '04 you will be able to choose something better than the current SRT-6, and you won't have lost as much money on the depreciation as well.
You didn't say over what amount of time that $300. more is for but I would assume that it probably is for at least a couple of years.