"For bonus points on the topic of altruism, do [you] think people can become to[o] altruistic and not do enough for themselves ?"
[Altruism: the belief in or practice of disinterested and selfless concern for the well-being of others.]
Yes it is most definitely possible, and occurs frequently with self-sacrificing people who habitually subjugate themselves for others (or another). However, usually such people are not masochists, but rather actually *believe (often falsely) that if they are patient enough, they will receive some sort of worthy reward eventually.
Likewise, altruism generally is very rarely pure in spirit, because most "altruistic" people are seeking some sort of reward for their work. Most often it is to bolster their self-esteem or their reputation / image in the eyes of others (seeking love and/or attention). And often enough, there are also ulterior materialistic motives for apparent altruism (needy or greedy).
That is because most social relationships are of some transactional nature.
Therefore, I'm convinced the allegory of the cave has very little (if anything) to do with the concept of altruism.
The allegory is more about using logic to free oneself from delusions (ignorance) and face reality (knowledge).
The cave-dwellers don't want to leave, because delusions (understandably) are often more (emotionally) tolerable for them than truth. Therefore the Cave (in many cases) is actually a psychological defense mechanism, a form of self-bondage or repression.
Whereas people who leave the cave voluntarily feel differently about it. They enjoy a rare freedom (and wisdom) that is bought at the cost of seeing things which might be emotionally unpleasant.
That is why wise people are often so somber or sober; and thus the saying, "ignorance is bliss". Yet the wise understand that bliss is not the same thing as freedom. Nor is bliss the same as Happiness.
And so, the fact that there is so much delusional thought and attitude attached to the subject of altruism, is confirmation enough that it is not what Plato meant to teach with the Cave allegory.