Equanimity as a factor of enlightenment is not totally neutral, but brings a sense of peace and healthiness. It a mind-state that does not get caught up in any experience, whether good or bad.
Thannissaro Bikkhu mentions "scepticism" as a useful tool toward equanimity. Not hot, doubtful scepticism, but not believing every thought that arises. Relating to them "with a question mark".
Equanimity is not the end goal of practice, but a tool to be cultivated. Thannissaro Bikkhu gives pithy, simple meditation instructions on how we can cultivate equanimity in practice.