Your individual state laws will likely govern how your coverage works in the event of a loss. I'm a licensed insurance producer in WA State and what's described as "Full coverage" really isn't. It's comprehensive/collision and there is usually a deductible involved. When you have a loss, coverage kicks in less any deductible that is required. the coverage certainly comes with a higher cost for monthly/annual premium. Most insurance adjusters calculate the value based on NADA guidelines according to your vehicle's condition and mileage. Our 3rd Gen 4Runners, while amazing as they are, are either approaching or surpassing the 20 year age mark. Insurance adjusters are like car dealerships offering you trade-in value. From a professional standpoint, it doesn't sound like paying the additional premiums will be worth it. It's probably better to stash the extra $$$ into some sort of account that will pay you, at minimum, 5% annually on your money. If you end up in some form of collision, you can have yourself a project 4Runner and look at buying a different 4Runner.
For the folks who has a metric shit-ton of aftermarket products, upgrades and customizations, those will need to be independently insured on your policy; like Ron White said in his stand-up special, you're not goign to get away with claiming that you had a Rolex stereo in your rig.
Another option to consider is looking into a company that offers coverage based on 'Agreed Value'; this is what custom/restored/classic vehicles are often covered under. I'm not appointed with or affiliated by any insurance company, but I believe that Hagerty and Grundy are the two most commonly advertised companies, but do check with your agent/producer to see if such coverage is offered.
The law firm that I work at recently had a client who had his car totaled and we fought the insurance adjuster to get a little bit more compensation for the vehicle but we had to show that locally (within 100 miles) that there were comparable vehicles in similar condition available that were higher value. It was a complete pain in the ass.