Possible blown head gasket on 1999 Subaru Outback

Is is worth getting my car repaired if I have a blown head gasket. My car has 166,000 miles on it.

This repair will run less than $1000, I’d say it is worth it. Make really sure to find and fix the problem that led to the blown head gasket in the first place. Occasionally head gaskets fail for no good reason, but usually there is an underlying problem, namely overheating.

That depends on if the gasket is blown or not. A head gasket may be faulty but that does not mean that it’s blown.
Blown denotes one that has given up catastrophically and in which the combustion chamber is breached or a section has failed which then allows coolant or engine oil to pour out.

A head gasket that slightly seeps coolant or oil is has a problem that is referred to as weepage.
Weepage is not that big a deal and can sometimes be cured by simply retorquing the head bolts. A blown gasket IS a big deal and depending on the circumstances behind this the engine may not be worth repairing. (Severe overheating for an extended spell, coolant diluting the engine oil, etc.)

I think that most of that decision depends upon the condition of the rest of the car.
As just one example, albeit a very expensive example, if you have not changed the transmission fluid every 3 yrs/30k miles, then the trans is the next big ticket item that will need repair, and the cost for trans repair/rebuilding could well exceed the cost of head gasket replacement.

Translation: If you have not maintained the trans as described above, then you should probably consider buying another car.

Other possible issues as mileage mounts up are things like worn-out struts and front-end components like tie rod ends, although the cost of those problems pales by comparison with head gasket and trans repair. Has your mechanic inspected those areas to assess their condtion?

The first problem I had with the car was this weekend when the at oil temp light went on after being in stop and go traffic for an hour due to road construction and an accident. I pulled off the road and checked the manual that stated that I could still drive the car. Stopped for a while, got gas and when I started again the light was off. The car temperature gauge has never gone beyond mid level. Thought it was OK but when I tried to go someplace this am, the same thing happened and the car lost power. Also. speedometer stopped working for a while and then came back on. I have an appointment with the Subaru dealer tomorrow, but know they will charge me an arm and a leg for anything they do. Should I go someplace else?