Most people do nothing and then have a tantrum along the lines of "What do you mean, you only cover $1,000 worth of tools?"

Yes, insuring $300k of tools is outside the norm for your typical homeowner's carrier. If you have $300k of coverage for $50/month, I would keep that and spend your time/energy elsewhere. I wouldn't spend my time shopping around for a homeowner's carrier that will give me a $300k endorsement for my tools. Maybe you get lucky, but how much do you value your time?