Enlightenment or salvation?

Early Buddhism seems to focus exclusively on enlightenment, and Nirvana, but at some point that seems to change, most obviously from Nirvana toward the Bodhisattva's vows to forego Nirvana in favor of helping all beings equally, but the goal of enlightenment seems to lessen in favor of 'salvation'. If that is indeed the case, then is that because of the influence of Christianity? Because salvation has always seemed like a Christian concept to me, as in 'saving one's soul'. But we Buddhists have no souls. So what are we saving? As if enlightenment weren't enough of a lofty goal...

affinities

It is not that there is no-soul. It is that such "soul" is not as important as let believe. There is the simile of the candle. What goes on from birth to birth is what goes on when we light a new candle with one that is going out.
Is the wax the same?
The wick?
The flame?
We bring the "karmic seeds" along with that "consciousness".
We need affinities to receive teachings and to be enlightened.
As I said, I would never take the Bodhisattva vow under any circumstance.
Similar stories are told about a number of Tibetan Saints as well, whom people don't at first recognize. In another Buddhist tale, the ascetic Upaka scoffs at Gautama's bombastic proclamation of Buddhahood, and takes a bypath. Just as it might be the case in such instances, stories exist relating how Upaka1 -disillusioned with family life- finally joins the Buddha, ordains and gets born in heaven to attain liberation.

The same 'lesson' is present in both Hinayana and Mahayana Buddhism. Ascetic Pukkusāti gets to share the cowshed with Gautama Buddha, whom he is in search of, but does not recognize him. In another Buddhist text, Gautama Buddha is about to enter a forest where three of his disciples dwell (Chulagosinga Sutta). Not recognizing him, a junior disciple prays him not to enter the forest in order to avoid disrupting the group's harmony:”When Jacob awoke from his sleep, he thought, "Surely the LORD is in this place, and I was not aware of it."”1.

FWIW

Affinities to the Teachings of Buddha

Yes, I agree with the statement above that we need affinities to the Teachings of Buddha or Buddha (during his life time). For example the notorious Angulimala before he met Buddha and became an Arahant. Angulimala was a murderous and merciless human being. As Buddha was walking towards the road leading towards Angulimala, all the people whom he met like cowherds, shepherds and ploughmen shouted to Buddha that Angulimala was in the vicinity. However, Buddha went along the road unheeding their calls. True enough, Angulimala saw Buddha and he also wanted to kill him. He took up his sword and shield, buckled on his bow and followed close behind Buddha. Buddha knew that Angulimala was near him and he performed a super powerful feat where Angulimala though walking fast could not catch up with Him ( though he was walking at his normal pace). Eventually, Angulimala asked Buddha to stop and the Buddha replied that He had stopped but Angulimala hadn't stopped yet. He was curious over this statement and asked Buddha to explain it. Buddha then told Angulimala that He had stopped forever from committing violence to human beings whereas Angulimala still had not yet stopped restraining from violence. At once Angulimala realized that Buddha came to teach him the Dhamma and he renounced not to commit any evil deeds again. Then, he became a bhikkhu. So, here we can see that Angulimala has affinity with Buddha. If he has no affinity, he would not be able to meet Buddha and become an arahant. He would continue with his murderous acts and be reborn in the woeful realm.