In terms of "more explosive", an empty tank would have more fumes in it. If the fuel system were not a closed system under vacuum, it could potentially be a problem, but all fuel systems now are purged by the EVAP system and kept under a vacuum.

If you were to get ignition inside a fuel tank, once the available oxygen was used up by the combustion process, the fire would go out. You need three things to support active combustion, fuel (gasoline fumes in this case), oxygen (air in this case), and heat. These three things allow the chemical reaction we call combustion.

As I said before, gasoline in its liquid form does not like to burn readily. It is the fumes that burn and only in concentrations between 1.4% and 7.6% which represent the LEL and UEL (lower & upper explosive limits respectively). Below 1.4% concentration and it is too lean. Above 7.6% and it is too rich with 6.8% being the stoichiometric (ideal) concentration. This is what results in the 14.7:1 AFR that so many gasoline engines are tuned to. All concentrations are by mass, not volume which is another thing to consider.

 

There's millions of cars out there with electric in tank pumps...when's the last time you heard of a car just driving down the road and suddenly explodes because the fuel pump sparked?

In-tank pumps typically are more reliable and longer lasting than inlines as well, since they're kept cooler by being submerged in fuel. It's also easier for these pumps to push fuel than to pull it, so having the pump _in_ the fuel is better for it than a foot away trying to suck through a hose.

Unless you're running a lot of HP, and you can't find an in-tank large enough to support the engine, you'll gain nothing by switching to an inline.

As for engine smoothness, the reason the CPIs don't vibrate as much are because they have a balance shaft in them (I think later models had two shafts, but I'm not positive on that..I never paid a whole lot of attention to 2nd gen trucks). The fuel injection system type isn't going to change the vibration level of the engine. IMO, no, it's not at all worth the effort to swap, especially given the problems the CPI system had.