To be honest, it looks like you want to make a pricey mistake. If you do what you propose, you will never see the benefits of the offroad suspension.

First, there is no suspension on offer that will perform better for the described use than the suspension you have already from the factory. It is not the same at all as the 5th gen (which is also enough to get the job done but sucks).

Second, you cannot do anything beyond select moderate trails (not all moderate trails) while you have an approach angle of 21 degrees. I am as experienced as anyone offroading a vehicle with that kind of AA so trust me, save your 5,000. You will ALMOST ALWAYS run out of AA before you run out of undercarriage clearance. The balance are rare, awkward cases. The 1-2 degrees you will get out of a 2" lift won't make an appreciable difference either.

Third, an offroad suspension will ride worse on road than an adjustable OEM Lexus suspension. The aftermarket equivalent will not only be pricey (dual adjustments, etc) but also a lot more cumbersome to use and will require a lot more maintenance. In my experience, nothing limits outdoor trips more than hassle. The less the hassle, the more the trips. Not to mention, aftermarket suspensions are often noisy, depending on which suspensions and what exactly setups.

Fourth, you can never grow out of shocks in the mountains of CO. You can crawl on whatever. As for the desert, no matter how stiff your suspension, you will always be cutting it close with the front bumper when you misjudge something. And a front bumper at 21-23 degrees AA will be destroyed the first time you make a mistake.

Lastly, I think that if you are serious about offroading, you need to be able to do the suspension yourself. And I used to be the guy who never took a wheel off a car (before I started offroading).

In short, you have a super nice vehicle as is. You can make a beast out of it, but you will have to start with the front bumper.

Good luck and happy camping!