I decided to finally go ahead and do my spark plugs. I noticed there wasn't a thread with a step by step with pics, so I thought I'd add one. I got a quote from a dealer one time for this job, and it was just under $500, which is insane and probably takes a Lexus tech less than an hour to do.
It's a straightforward job, more difficult than an oil change or brakes, but MUCH easier to change plugs than most modern cars.
I highly recommend getting a set of spark plug sockets, the kind with a rubber retainer inside. You also need a set of socket extensions and flex joints. The most difficult part of the job is the angle going in and out can be tough, the right length of extension makes all the difference. Also, the consensus seems to be you should always do this job when the engine has cooled down so you don't pull the threads out.
The spark plug I used was Denso Iridium SK20R11. It is the factory plug and what I would recommend. You can buy them for around $10 a piece at Amazon or RockAuto.
First thing is to remove the engine cover, it's held on with two 10mm bolts.
Next you'll see you have a fairly clear path to get to them.
The Passenger Side has a few things in the way, this black box tied to the air intake and the car battery. I was able to install only taking out the black box with the intake hose.
Remove the black box, it's held down by a 10mm bolt, 2 vacuum hoses, and an air intake hose.
Now you also have a clear shot at the passenger side.
Next, remove the coil packs, each one is held down by a 10mm bolt. I prefer to do it one by one so there's no mix up. You can either unplug them by the clips, or pull them out with the wires still connected. Just be careful to make sure you have enough slack when you pull it out of the way.
This is was the tubes look like when you pull them out
Next, take a 5/8" (or 16mm) spark plug socket, and with an extension, place it down the hole and turn counterclockwise. There should be very little resistance, just make sure its seated down completely as it takes some downward pressure.
After removing, inspect the spark plugs. Mine were actually in decent shape, EXCEPT for the one that was the most difficult to get to, on the passenger side closest to the firewall. My guess is the dealership that did the job skipped it, thinking no one would ever inspect his work.
A great way to put the spark plugs in so they won't get cross threaded is to get some 5/8" heater hose at an auto parts store, and place the plug inside. The hose fits the tube perfectly, and keeps it centered. Put the spark plug down the hole and press down firmly, then just keep hand tightening clockwise until the spark plug seats. This is a great way to make sure you don't get it cross threaded. Once it's seated and you can no longer turn the hose, I then remove and put a spark plug socket on, and turned it an additional quarter turn. The factory manual rates it at 15 ft lbs. It's very little torque.
I then took a little dialectric grease, and placed a small amount on the tip rubber boot that has the coil pack that adjoins to the spark plug.
I then seat the coil pack onto the spark plug, press down, and put the 10mm bolt back in. Be VERY careful about putting the coil pack bolt in. It's very easy to get it cross threaded and your screwing it into aluminum. Make sure the angle is correct, I would hand tighten and then just torque until it's snug.
The only plug that is a bit difficult to get to is the one on the passenger side, near the firewall. Even still, I was able to remove it without taking the battery out. Again, I found this one had looked like it had never been changed, so it had almost 150k miles on it.
After finishing, check your work and make sure all the coils are attached, with the weather clips snapped in and the coil packs screwed in. Make sure the packs are flush against the block. Then put the "black box" back in, attach the intake and vacuum hoses, then attach the engine cover.
My guess is the first time you do this job, count on it taking about 2-3 hours. After doing it once, most people could easily do it it in around an hour. I would go very slow and take your time, you don't want to cross thread the spark plugs into the block or the coil packs.