This is a question only you yourself can answer. If the vehicle is not costing you a fortune to maintain and gets you where you want to go safely, then drive it until it dies. This will give you more time to save up money and shop to decide what car you want as a replacement. If you are going to buy a new car, waiting generally means a better product will be in your future. Areas that are always improving are safety, refinement, ride, handling, braking, comfort features, fit, finish, materials, etc. Fuel economy can improve but usually doesn't dramatically unless there is a major technology change, such as going to a hybrid or diesel, but that's another story altogether. Not all vehicles achieve superior results as each generation is replaced by the next, but the better car companies generally improve products over time.
if you have a unique used car you want, waiting might not be a good idea because you might not be able to find that car later. If your Jetta dies, it will likely have less value, depending on the overall condition of the car, it's desirability as a car to rebuild, etc. Of course, a car that is nine years old is depreciating slowly, so time doesn't cost you much unless there is catastrophic mechanical failure. Waiting to that point isn't good if you are forced to make a quick decision or you won't have transportation.
Remember, transportation that is neither reliable or safe makes no sense at any cost. With the high cost of auto repair labor, unless you can do a lot of the work yourself, you will unlikely receive the benefit of major repairs because virtually everything wears out given enough time or miles.