What a lovely GTS!
Here are my very humble views from my Dino ownership experience.
SCM 246's list is highly interesting. I will most definitely apply it to my GTS. Thanks, SCM! This will make for a very good start when going long distances at a good pace. Terry's advice on the accelerator spare wire is also spot on for any classic (been there too).
Mind you, I did 10.000km at very high pace mostly in the mountains, in three and a half weeks without any of these clever little upgrades, just a very thoroughly checked and refreshed original 58.000km Dino before I set off.
Going through and refreshing the car also encompassed hard testing on my back roads which triggered two additional garage visits for corrections, adjustments and one tiny repair work. Later, on my 10.000km tour I had no issues apart from a burnt radiator fan which caused no disruption.
I did one point on SCM's list when going through the car after purchase and that was checking for oil drippage on the alternator and it's not yet an issue but will be.
Also check the fuel line which interconnects the tanks. It rots and must be replaced!
I am occasionally thinking of power upgrades for my Dino but it always ends with a sensible nothing. I use my 308 for such perversions.
I have taken my Dino to the test in the company of modern Ferraris and on the most curvy roads it can hold up quite well! Never forget it is a very well conceived car capable of surprisingly high pace if everything on the car is 100% in order. Few classics can outpace it when the road gets really twisty, my word.
I would absolutely not drive more than 50.000km without overhauling the steering, shocks and changing the springs and bushings. If you almost only drive it hard I would bring that interval down to 30.000km as an absolute maximum. It is my humble view that a perfect steering is key to make a Dino go fast. The steering is its major way of telling you what it needs to go fast and boy does it have a good steering!! If you concentrate on setting up these simple road holding points to 100% you will not need the extra power, trust me. A good thing to do as well is to pair the road holding setup with hard track time.
You have great knowledge I'm sure from your track time in your 355 and 360 Challenge so forgive me if I'm stating obvious information. Anyway, here go my views.
If you put 16" wheels and modern tyres on you must upgrade the brakes and you must absolutely make sure the whole suspension is up for it. In fact you'd probably have to take it to the next level by installing modern shocks, stiffer and lower springs and move to semi-hard bushings. This will likely make it faster than with a 30hp upgrade and no road holding upgrades.
My new Dino specialist in Vevey builds racing Dinos and racing 308s. He does the porting job on the heads with cam upgrades but like Terry says, now you're moving into big money territory. It certainly makes the car go and according to this guy in Vevey it actually runs better all trough the rev range but of course it needs to be paired with a carburettor upgrade and an exhaust upgrade. The Stratos carb upgrade has such tall intakes that you can't close the hood without mods or leaving it half open for better air evacuation. The Stratos setup has a huge advantage however; you get totally rid of the fuel starvation at constant mid throttle during high speed left cornering. Apparently the stock engine works fine in the Fiat Dino due to its longitudinal position where this highly annoying syndrome doesn't come into effect.
The a/m power upgrade is surely great but for constant high pace it's worth little without the road holding upgrade. But let's not kid ourselves, with both upgrades the Dino becomes a very sharp track and hill climb tool. The question is: Are you prepared to part with the money required and are you prepared to part that much from the original Dino with all its charms?
Perhaps buying a second Dino in a sorry state and turning it into your hill climb racer is the way forward? That has certainly gone through my mind but right now I let that modification yearning go into my 308. Funnily, also on the 308 I more and more see no point in power upgrading apart from the high compression pistons it already had when I purchased it. What comes next on the 308 are the a/m road holding upgrades and little else, which should make the car very fast on the mountain roads!