Crazy mental first question. While the engine is open and the cams are on show how difficult/what's involved to change the cams for some say...... GTA cams ???
pkr was talking about the clips, of course, not the cams
If you were changing the cams you'd obviously need to re-time, with the locking blocks (these seem to be hard to get for the GTA engine). You're right that changing the cams would make more difference than any other modification that's practical to do (except, maybe, fitting a supercharger or turbocharger
Bear in mind that cam timing is always a compromise between low-end torque, fuel economy, emissions, and power... and without the extra capacity of the 3.2, I can't see there being much of a gain for any of these factors. Actually the valve timing for the standard GTA (it's still a road car) might be more or less identical, with the gains coming from the extra capacity. I'll check my 916 book
Someone would have spent ages deliberating over the valve lift/timing/duration/overlap for the cams that you have. Unless you're happy to change the engine's character substantially for track racing, it's probably not worth it.
E.g. If you increased the compression ratio a bit and put in a more racing-style reground cam (more valve overlap) to go with improved air intake and exhaust system, you could lift the top-end power from 220 to 250 (or more), but below 2000RPM there would probably be less power than standard, making the car more difficult to drive in street conditions. Could still be rewarding when driven hard. In England, insurance would be something else to consider? Just general advice for thought/discussion...