Worth fixing??

I would fix it if the rest of the car is in good shape. You can't get a decent car for $1,000.

Most of the time a fix is cheaper than a new payment for another car.

It's unfortunate that your wrench didn't replace the t-belt tensioner and idler bearing when they were off when replacing the head gaskets. Another $100 in parts would've prevented this failure, alas.... That said, the real time required to replace the belt, idler, and tensioner is 4-5 hours max, with $200 in parts. It's a pretty easy $600 job. The problem is indeed that a valve PROBABLY was bent if a failure occurred at speed, tripling the repair cost because of all the head work. Given its age, and the fact that it's a wonky-handling Forester, I'd start over again. Your 4EAT tranny would probably be next, and that's another $1.5-2k used installed. Say goodbye....