You post an interesting question. I basically have the same problem. I have a 1994 GS300 and that car has been very good to me! It has been in California since 1995, I have passed every smog test since then although the last one was a struggle since the engine light was on. I simply disconnected the battery, the light went off, took it down for a smog test and it BARELY passed. Good for 2 years until July, 2015.
My car has some problems too. The power steering pump leaks and I had the high power hose replaced because they thought that was the problem. But power steering still leaks. It doesn't start on occasion although I have a new battery. I'm told it could be the starter switch, the actual starter or the solenoid. The hood and trunk won't stay up and the radio antenna motor is dead, It has 189,000 miles on it, I am told to use premium gas only.
Now, the good things: Runs great, the engine purrs. Does not use oil at all and had my last oil change a year ago simply because I have only driven 3,000 miles in the last year. It has the premium audio system and a 12 CD changer. Sometimes I find my self sitting in the car just listening to the stereo to relax. The body is almost perfect with just 1-2 minor imperfections. The gold color is very classy and the rain still bubbles up like it was just waxed. The leather interior is basically new but there is some wear in the drivers set. The AC and heater work great. The power tilt wheel, power side mirror and power drivers seat work like new.
So, what do I do? Do I spend $1500 to $3000 fix it up so I can continue to drive 3000 miles a year or just drive it until it dies? Do I donate it? Do I put it in the garage and wait for it to become a "classic?" Do I sell it to the highest bidder...Kelly Blue Book says it retails to a private party for $1800 and $2200. (I have a 2002 Toyota Sienna with no problems that I can drive also.)
These are questions that an inquiring mind would like answered.
Since you posted the above, what have you done?
I know one thing: It's going to take a lot before this well made Lexus just dies. I talk to Lexus owners all the time and we all agree that Toyota broke the mold when they made this car!