Will it be used as a daily car or are you just saving it for the weekends?
How important is it that the car retain it's reliability and economy?
My initial gut feeling would be to investigate a supercharger kit for it. Those V8 engines have a lot more to give.
The best mods for a car engine are as follows.
Internal work yields the biggest gains, head work like porting polishing and 3 angle valve jobs will maximise the airflow and raise the power.
If you want to go to the max then cryo treat the block, get it rebored and look into blueprinting and balancing as well. You'll also need stronger internal parts if you are looking at a big power hike so forged rods etc.. are the order of the day.
Bigger valves are an obvious add on but not all engines are suitable as it depends how close together the OEM valves are.
A fast road cam will yield good power gains, especially in the top end of the rev range.
Don't go mad though a profile of up to 270 degrees will generally give the best gains without the engine becoming cammy (lumpy tickover at low RPM). I don't know much about Maserati Cam profiles though so can't really offer specific advice here.
The most popular power mods are induction kits (which are questionable as power mods and the standard Maserati Airbox and exhaust will work just fine unless you bump the power up by a large order of magnitude.This also applies to sports exhausts with sports catalysts or decats.
To keep the car legal I'd recommend a sports catalyst rather than a decat.
The last mod should always be a remap as this will allow you to fully realise the power gains on offer from your mods. Turbo cars respond very well to remaps.
It's worth having a read of the articles on www.torquecars.com/tuning/ for more information on these mods and what the terms mean.