What are Mormon ordinances really for? And are they needed?

Is a ceremonial act going to save us and send us to heaven?

No. But the behaviour needed to keep the covenant might.

Matthew 25, the parable of the Goats and Sheep, describes the righteous, those who will have eternal life.

Come, ye blessed of my Father, inherit the kingdom prepared for you... These shall go... into life eternal. (v. 34, 46)

What acts had the "righteous" done? Ordinances? Strict obedience?

The simple description is of people who had fed the hungry, gave drink to the thirsty, took in the stranger, clothed the naked, visited the sick and the prisoner. They had served God by serving their fellow man. "Inasmuch as ye have done it unto one of the least of these my brethren, ye have done it unto me."

Importantly this is not after an initial triage of checking membership cards. The parable starts by saying:

Matthew 25, the parable of the Goats and Sheep, describes the righteous, those who will have eternal life.

When the Son of man shall come in his glory... And before him shall be gathered all nations: and he shall separate them one from another

So what are the ordinances for? It seems to me that all of the covenants are a promise to serve God by serving others. In this service we develop charity and become more Christlike. To paraphrase the Givens, ordinances do not offer us the option to walk the 4 or 5 gates carrying some "celestial hall-pass" (to quote Givens2).

If you look at all of the ordinances, they are promises to serve God by serving other people.

Baptism
Sacrament
Priesthood
Endowment
Marriage

I think God is less interested in the ordinance and more interested in the commitment being kept that was made during the ordinance.