From the aspect of starting over with the existing world, we've depleted most of the much easier resources we had to work with the first time around, so the second climb up technology's ladder would be far harder, maybe even impossible. Reuse and salvage is one route we would take, but some materials can't be. Either they can't be recycled or reclaimed, or like some alloys we've made can't be just melted down and reused, some even can't be reshaped. So many things require an existing and running infrastructure to just make these things.

The first episode of James Burke's Connections series touches on this. Things we don't even think about that support civilization because we've built up around them for centuries, and a lot of it in the most recent century. Starting from base level is far more difficult than the first time around... and like I said, before we had much different resources around us to support the growth.