Shimano made several levels of Exage, all of them pretty low end. But even the lower end Shimano stuff seems to work pretty well. Regardless, without pictures, but described as really good condition, $150 sounds like a deal. I am assuming the PS20 is a Canadian model, I can't find it listed in US models. What is the frame tubing? Even with relatively mediocre tubing, sounds like a pretty good deal.

At full market pricing, you are not going to get much of a Japanese bike (or any other road bike) at that price level. The good ones bring over $200, with indexed shifting, more like $250 to $275.

Around here, if you picked up a bike like that for $150, and later found something better, you could easily get your money back out of it. I have done this myself several times over the last couple of years, upgrading my rider from really low end to something pretty good. That's the beauty of buying used at an attractive (below market) price.