When, if at all, are Insulation Resistance (or Megger) tests on an electrical system useful?
I would be more worried about fused breaker contacts and damaged breakers from the lightning surge. I can't say whether or not lightning damaged your wire insulation but megging isn't a guarantee either. $150 per circuit is highway robbery. Sure there is labor involved but no more than a few hours at most.

As for the circuit breakers, depending on your panel box, it might be cheaper to replace them than bother testing them. Testing requires calibrated equipment which is expensive and not in a standard electricians tool box. They are only a few bucks each anyway.

The important question is how long ago was your last lightning strike? If it was years ago and everything has been working properly, I'd leave it alone.

I was the victim of a strike some years back. An old TV antenna on the chimney  was struck. The surge blew out my TV, PC and a few wall warts. Thankfully the devices that were blown were switching supplies with enough isolation that the surge blew the mains side. The TV and PC required new power supplies. The wall warts were cheap. Didn't bother megging anything as the current took the short path through my TV and computer. Did all the work myself.

My "forensic analysis" revealed the antenna wiring allowed the surge current to go through an antenna amplifier to the 120V outlet and on to other appliances. I had the antenna removed when the roof was redone that same year so its a non issue now. I also bought a bunch of quality name brand surge protectors for my more sensitive/expensive appliances.

How do you protect your home from lightning?
If you have/need an antenna, get a good lightning arrestor on the line with a very secure connection to ground. Same goes for coax cable for cable TV and the like. And by secure, I mean a wire ran right to a ground rod or water main. Not some jenky "wrap wire around the nearest pipe looking thing" I see a lot of cable techs make. It's also helpful to get a ground line from a rod ran to the antenna. Give the surge current the fastest, low impedance path to ground. Use green #10 gauge wire for the antenna/cable wires and #6 bare copper for the antenna mast. Next up is to ensure your electric service is properly grounded. You may need to hire an electrician for this. Ensure the panel is properly bonded and all ground wires are in fact connected. Next up is to make sure all of your pipes are also bonded and grounded. Things like jumpers for gas, heating and water pipes. And if you are in a very strike prone area, perhaps lightning rods on the roof would be a good idea. Buy quality surge arrestor outlet strips or wall adapters; no low price junk 99 cent store specials. And finally, a whole house arrestor isn't a bad idea either as long as it is a good name brand.