I've thought of another thing that can shorten the life of a capacitor: ripple current, the AC current flowing through the capacitor. If a capacitor is used to decouple a speaker or is placed across the rectifier of a DC supply the ripple current can be considerable which will cause heating and distruction of the capacitor if it's too high. In this case, chose a capacitor with sufficient ripple current rating and the lowest ESR and ESL specifications you can afford.