I'm not sure but at 170k, if the head has never been touched, then maybe the guides need doing, but then with such a long history these cars have now, who knows if it hasn't been done at some stage. Others might see it differently, but if it was my car I would just have new valve seals fitted and see how it goes. If the guides are worn I believe it will tend to chop them out quicker than normal, and then you can plan to pull the head off. The seals are cheap (check autohaus) and not that much labour - less than $200 all up? My thinking is that would be worth a try. Doing the head must be at least $1k involved, but if you plan to keep it and do lots of miles then it will last for a long time.
Just my thinking - hope that helps.