When you turn on the key you should hear the fuel pump run for 2 seconds, listen for it.
Next time there is a No Start, listen for it, it isn't quiet.
You can turn the key off and on as many times as you want, won't hurt anything, fuel pump should run for 2 seconds each time key is turned on.
Yes, if inertia switch was the problem fuel pump won't come on.
But no, that would not be a symptom of a bad inertia switch, they either work or don't, without resetting them, it wouldn't start working again after sitting.
Outside of a failing fuel pump, which can be intermittent, are there any other clues?
Anti-theft light normal?
It does disable fuel if tripped
Dash lights and gauges still working after engine dies?
So power is not being cut
I guess the quickest way to find a direction would be a 50/50 test
Get a spray can of Quick Start(ether)
Next time you have a no start, pull off Power brake booster hose(or PCV hose) and spray some into the intake.
Put hose back on and try to start engine
If it fires up and dies then fuel is your problem.
If it doesn't fire up then it is the spark that is not working.
If you don't hear the fuel pump when key is turned on then that would be the problem.
Next step would be to use a test light on the inertia switch, since you know where that is.
Ground the test light and hold the other contact on either wire on inertia switch.
Turn on the key, light will glow a bit
Then get bright for 2 second and then dim again, that means power is going to fuel pump and if you don't hear it then pump is bad.
Could be a wire but 99.9% of the time it is the pump.
If light doesn't get bright then replace the Fuel Pump relay, in engine fuse box.
Standard relay, costs about $6