In terms of engine work, I'd be more interested in something like a Power Commander V with the "Autotune" module so that it had better ability to adapt to things like dramatic changes in altitude, ambient temperature, fuel quality etc., on the fly, rather than needing an engine remap. To me, that's a feature that seems more relevant on an adventure bike than outright power hikes.
Likewisem, rather than trying to compete with sportsbikes for high end BHP, I'd be more interested in increased torque for lugging lots of gear and a pillion. To be fair to the GS though, it already copes very well with this in terms of how little difference it makes to the ability to accelerate etc. considering the fairly modest power output.
I like my bike because I can overtake 4x4s down farm tracks with a week's worth of shopping on the back.