But what about first century sources like the apostles and St. Peter and other eyewitnesses. The resurrection claims go back to the very earliest extant writings about Christianity for example.
I read about a study once. It related to people belonging to modern apocalyptic cults, you know the type 'the world will end on December 12 2013' type cults.What the study found was that the fact that the world didn't actually end didn't damage the members' faith in the cult, it often made them stronger.
If you are emotionally invested in something, your mind needs to react to the cognitive dissonance of being 'wrong', which can be done by either admitting you were wrong, or by reimagining the situation in a way that makes you 'not wrong'.
Jesus' resurrection could have been a response to this. Perhaps it was a metaphor that gained a real world backstory over time. Perhaps an apostle had a vision/dream that lead to the tale.
This is just speculation, but it is at leat possible that his death had to be explained away to remove cognitive dissonance and that this was a result of it.
The other miracles, healing the sick, feeding the masses, etc. are pretty par for the course and have been applied to many figures. If you watch modern faith healers you see that they have 'miraculous' powers from god. Most of us know better now, but back then an illiterate peasant is unlikely to have been well versed in sceptical thinking.
Many stories probably do have a basis in reality but they just became embellished over time, even over a short time scale. We can see this in regard to all kinds of historical figures, Jesus is unlikely to have been the one person in ancient history whose followers really told it exactly like it happened.