Some good questions there. This is going to be a long answer!
Boost affecting performance
Combustion engines - petrol too - use fuel to burn, and need air to burn that fuel in. It comes down to a hydrocarbon (petrol/diesel) being ignited in oxygen (about 20% of our atmosphere). If there's enough oxygen, all of the fuel is burned during the "power stroke" and what comes out of the cylinder is (ideally) carbon dioxide and water vapour (C12H23 + 18O2 = 12CO2 + 12H20 roughly). Slightly less air and SOME of the fuel is partly burned = black smoke (soot). Next to no air and MOST of the fuel is unburned (white smoke). Too much air and you're burning all of the fuel, but the equation has a little O2 coming out as well - not ideal for power if you're fishing for every last bit (eg for racing) but good for economy and the environment.
Boosting increases the amount of oxygen available (making the air denser, cramming more oxygen in). This does two things: it ensures that all of the fuel is burned, yes, but also allows you to increase the amount of fuel so that even more can be fully burned during the power stroke = more power. So more boost + more fuel = more power. Within the limits of the engine and its setup, of course!
Intercooling cools the air. Heating the air makes it expand - less molecules of oxygen per millilitre of air - so cooling that air (and maintaining the pressure) crams even more oxygen in, which in turn allows even more fuel and therefore more power. There are caveats to all this and the biggest one is the pressure that you can reasonably maintain in an intake that has a path connected to the chassis AND the engine where the engine needs to be able to move a bit - which means rubber or silicone hosing and clamps. They're weak points if you're looking to boost high.
So boosting gives you more air, which gives you the capacity to increase the fuel and therefore get more power (boost alone will NOT give any more power, because if all of the fuel is already burned, extra air does nothing). More power is more acceleration OR the same acceleration for less input (more economy).
Offroading and power
It is true that there are times when you're off-roading that you'll need more power. The Dakar rally is proof enough of that. But there will be many, many times when you'll be on a track and will just want to gently apply the throttle so that you only just move a little without spinning the wheels, particularly important when climbing steep slopes. I'd suggest that our utes have enough power for most of what we would normally throw at it in our forests and beaches.
Preparing for more boost
You can upgrade the intercooler, which will "densify" the air further without increasing boost and will provide more air - but without adding any fuel, your performance gains here will be marginal (and perhaps a little deflating if you were looking for huge gains).
To increase the boost level, you will need to consider an alternative intercooler anyway. The V9X in particular has a intercooler that has a weak area and several people have had theirs "balloon". Add in better piping, stronger hoses, better clamps and then look at fuel - perhaps a chip, perhaps LPG or even both if you're really trying to get some beans out of it.
Caveat on more power
Our engines are designed - that is, bearings, conrods, cylinder head construction etc - for a certain amount of power. There's obviously some leeway which provides for small anomalies creating conditions where momentarily more power is available (eg overfuelling and overboosting for a fraction of a second). With this in mind, the engines are expected to last for a certain amount of time.
Increasing the power will increase the strain on everything. There's no escaping it. Hopefully you aren't considering anything as extreme as a top fuel dragster which has its engine rebuilt every race!
Underfuelling and overboosting
Not enough fuel will reduce your power. Power comes from fuel that's given enough air to burn completely (and quickly).
Overboosting is more likely to cause hoses to pop off and then you'll have NO boost at all, and if the engine is tuned to handle certain fuel and boost levels, your available power will disappear instantly - I had my charge air hose pop off the intake manifold once on the Putty Road and my caravan disappeared in a cloud of black smoke while we slowed to a crawl.
Hope that helps answer your questions!
