I ripped out the AHC on my first LX, a 2004 Blue Vapour metallic, for a Tough Dog set-up. The biggest mistake. I ran the big bore shocks in the front and the foam cell adjustables in the rear with a medium spring. I even went to the TD factory for a look(crappy warehouse) as it is only a few hours away here in Vic. Had the work carried out by Opposite Lock who were great.
It absolutely destroyed my LX. The ride was choppy and awful, laden and unladen. It took months to settle and pushed the fuel economy on the highway from 11.7 to 20.L/100kms. It ruined the car, I just cracked it and traded it for a 200. Incidentally I didnt enjoy that either and am finally happy back in a cream puff LX470 with totally new AHC.
I reflected on it considerably and came to the conclusion that low budget aftermarket suppliers can't compete with the r&d and engineering dollars that Toyota puts into the development of it's systems. AHC is bulletproof and I only ripped mine out due to the jitters I got on mud about failures. It only needs attention once a decade and the refurb of my current system wasn't expensive at all. The ride is sublime for a ladder chassis solid rear axle vehicle and I like the fact it lowers at highway speeds for fuel economy.
Tough dog might be suitable for a basher 80 series thats given hell everyday and where ride quality isnt a requirement. After the whole experience though it was jittery low budget peasant horse cart setup.
Basically unless you are rock crawling or heavy duty off roading and you still have AHC, i'd do everything you could to maintain it and replace as required. If you can afford to fuel it you can afford to maintain it's robust AHC system.
I approached ARB for an OME kit initially and they told me they can't do Lexus'....even though they had a Sahara gettings its AHC ripped out as I was there. Smh.....
Anyway just my experience with TD. (I've seen their R&D center). Hope others are having better luck.