If you plan to keep the car for any length of time, suggest you have all this work done.
Many manufacturers are specifying 100K for spark plugs. Here’s the problem. Part of their motivation for this high number is the car rating magazines include how much maintenance expense is to be expected if you own the car. And the magazines use the manufacturer’s suggested intervals to cost that out. Now if you wanted your car to come in showing a low cost maintenance in comparison to other cars, what would you do?
100 k is too many miles in my opinion for spark plug changes. It’s not that the newer-type plugs won’t last that long so much, but that they can get coated with very stubborn carbon deposits and can become difficult to remove without damaging the threads in the cylinder head. If that happens the replacement spark plugs might not be able to form a tight seal, so expensive cylinder head reconditioning will be needed. The other problem is that the plug gap can widen over miles driven. Modern fuel injection/electronic ignition systems compensate for this by raising the spark voltage. But that can overheat and damage the coil or coil packs. Coil packs are a lot more expensive to replace than spark plugs.
Valve adjustment. Think positive. It’s possible all that needs to be done is measure it, all the valves will remain within specs, and no adjustment will be needed. That won’t be very expensive. Ask what they’ll charge if no adjustment is required. On my 4- banger Corolla that job takes about 45 minutes to do. A pro could do it in 30 minutes or less I suspect. If it turns out no adjustment is needed, then you’ll know the valves are fine, plus you’ll have a baseline to compare with for the next valve measurement.
If you don’t do the valve measurement, since it isn’t in the manufacturer’s maintenance schedule apparently, most likely no harm will be done. I’ve measured the valves for years, first on my 70’s VW Rabbit, and my 90’s Corolla, and never once has an adjustment been required. I just write the numbers down in the book, verify they resided within the spec limits, and put it all back together.
But what if you don’t measure them, and one or more actually they are out of spec? If the valves are a little too loose, the worst that happens usually, besides some noise, is you lose some engine power. Takes longer to accelerate. But if the valves are too tight, especially one the exhaust valves, that can be a bigger problem. A tight valve wouldn’t properly seat, and some combination of loss of compression and improper heat transfer could occur, the latter of which could badly damage the valve and/or the seat.
So what would I do? At 100 K, I’d measure the valve clearances.
If you want to take a chance, and haven’t noticed any performance loss, and tend to not do hard accelerations or other driving styles that might be causing hotter than normal conditions inside the engine, you can probably get away with skipping the valve clearance measurement. But I wouldn’t.