This is the 5th vehicle now with leather seats for me. My experience/methods:
* Leatherique is really good stuff, but it doesn't do a really deep down cleaning if your seats are filthy or neglected. I use it annually, I really do like it and the results. You need a really hot sunny day to "bake" the Rejuvinator oil into the leather, park it outside with the windows up, I use a remote thermometer to keep an eye on the interior temps. Once it drops back down below about 100d, I give them a good with with the Cleaner, they really do come out nice and feel great. Nice smell too.
* I highly recommend subbing to the AMMO NYC channel on YouTube, then take a look at his videos on interior cleaning. This guy is a fanatic about cleaning/detailing.
* I need to do the seats in the 200 and my wife's IS, both if which we just bought and are at the point that they need attention. Cleaning the dirt out of the perforated leather (if you have cooled seats) is a PITA, Leatherique won't do this. I have found the best way to get them really clean is to first give them a good vacuuming with a strong shop vac, then use a steam cleaner. You do have to be careful not to overheat the leather as some actually have a thin vinyl coating that you can melt. Just go fast, make several passes with the cleaning brush wrapped in a MF towel until the towel stays clean. Just plain water in the steam cleaner, this is the one I have:
Amazon.com: McCulloch MC1375 Canister Steam System: Home & Kitchen
Very useful tool, excellent for cleaning off smudges and grime from plastic. Great for getting stains out of carpet and headliner.
* If you steam clean, be aware that this leaves the leather very clean but strips out the oils, so you need a treatment to keep it soft. Lexol is decent, my favorite is actually the stuff they sell at the Lexus dealers.