95 Lexus LS400 smokes and now hesitates

I have a 1995 Lexus LS 400 with the V8 engine. The car is almost at 150,000 miles.
Recently, the car has started to blow a lot of blue smoke in the mornings - but not every morning. After a few minutes there would be no more smoke. Recently, at the end of a 70 mile freeway drive, the check engine light came on. When I got onto city streets, the car was running rough, as if it was missing. I thought perhaps I had a loose wire. I took it to my mechanic and left it for the morning. He callled and announced that two of the spark plugs were coated with oil, that they had cleaned the plugs and reset the computer.

We have been discussing the need for a valve job or doing the valves and the rings in the near future. Rough estimates are in the $2,200 to $2,500 range. All of a sudden, I'm having misgivings.

First, the check engine light came back on almost immediately. The car runs very rough in Drive, but if I put it inot 3rd or 2nd, it seems to smooth out. Other times the light will blink.

Should I even be driving the car? I was hoping to get to and from work for one more week. After that, I have to go out of town for a week, and they will have plenty of time to work on the car.

I'm also concerned that their original diagnosis was a little too cavalier - maybe I just need the valves done and not the rings - maybe the repair is in the neighborhood of a few hundred dollars, not thousands.

What are your thoughts?
Hardy