When I bought my 1998 I thought I would keep her a year for kicks and grins and buy something newer like a nice 997 Turbo. That was nine years ago.
We all make choices. I am one of those crazy guys that believes in driving them til the wheels fall off, fix em, and drive em some more. I am in the minority.
I currently own 7 cars, 4 motorcycles and a boat. 2 cars are at 100k, 2 are at 180k, and 3 are at 250k+ miles.
I figure if you want to own em, it's always cheaper and more flexible to fix and maintain em than to buy new and have 60 months of car payments. If I run low on cash and one needs fixing, I just roll it into the garage until some cash frees up. I don't have that flexibility with new car payments. Banks frown on missed due dates so you are locked in to a guaranteed expense every month.
That doesn't mean I never buy new but I shy away from it these days. I like freedom and flexibility with my cash. If I decide I want a new car, I'll go get one but I sorta like playing with the older ones.
Bottom line: If you like the car and want to keep it, take it to a good indy shop for a thorough preventative maintenance inspection. A good shop will carefully evaluate the car and give you some real $$$ numbers as to what you will need to spend to correct any deferred maintenance or problem areas and get it reliable. If it makes sense, get her fixed. If not, sell her and buy something else. It can work both ways but it's always best to choose the one that most likely allows you to sleep well at night.