You are right.
First of all, the lexus is300 was build by toyota, wich mean reliability. But as everything ages, the car will too. And the problem with such a car like the is300 is, if you have tough to buy it as a project/daily/fun car, well you are not alone. Avoid to buy a used one from some guy that have " chaged projects " and thing like that. Sometime buying an old project from someone else can be a lot of trouble. And why do you think people sell their project. Because it would be costy to repair.. But there are some rare gems aroun.. You just have to find yours! Buying from first owner could be great ( if they took care of the car ) and even some young folks can have a good is300. Look at what have been done on the car. If it stills have the original engine, what mods does it have and what care was don by the previous owners.
Good luck in your shopping