Is the repair worth it?

I’m not sure if I should invest any more money in car repair. I have a 2002 mercury sable with 180,000 miles on it. My check engine light was steady yellow for some time (I was told it was just a sensor). I had noticed in the past couple of months that the car took some time to accelerate to when driving on the highway, it could use rear break replacement and with my last oil change I was told I had some oil leaking. Recently after starting and driving less than a ½ mile first the engine light was flashing yellow then turned to a flashing red which I assume was a misfire. There was also some vibrating holding the steering wheel. It was diagnosed as needing a new ignition coil as the immediate repair. I don’t mind investing in the cars maintenance, but I’m not certain the repair of the ignition coil is part of a larger problem. All things considered, is it worth invest more money in repairs?