Sorry, guys, I gotta chime in here and fix a few budding misconceptions.
First, failure of a capacitor operated below its breakdown voltage, or production of a flawed one, of any kind anywhere, is quite rare. I've been working with electronics since I was 9 years old (that's 48 years ago) and, with the exception of electrolytic caps, which have no relevance here, I can count, on the toes of one foot, the number of failed capacitors I've seen. If you have a capacitor problem, it is almost certainly a bad connection, pinched wire, or something similar.
Second, I can't for the life of me see why a higher or lower capacitance would cause points to have a tit in one direction or another. This is electromigration, of a sort, and it depends on the direction of current during the first few microeconds after the points open, while they are arcing a bit. This is not affected by capacitor value. The capacitor value will change the magnitude and frequency of the voltage/current waveform in the circuit, but not its polarity or its overall shape.
Capacitor value does not change the energy available for a spark, either, but it will change the peak voltage. Less capacitance means higher peak voltage but a burst that dies off faster. Possibly you could use this to fine-tune the ignition--or maybe not; depends whether the important quantity is voltage or energy. The caps intended for a particular ignition system don't come in multiple values, though, so this all seems academic. I suppose you could use radio capacitors, with a little creativity, or ones intended for other cars, if you can figure out the value. They're not marked.