Concrete doesn’t have to be completely crushed. You can always use it as urbanite: http://www.terranovalandscaping.com/blog/2007/02/07/90/
It’s probably easier to reuse pavers, but, unfortunately, pavers are more expensive. So maybe it’s a matter of identifying areas that are likely to be used farther into the future vs. those that are likely to be torn up eventually. Then you can use concrete in areas less likely to change, and use pavers where there will likely be a reason to tear out the pavement, like over pipes that might break. That way the upfront cost of the pavers might be offset by the fact that they can be re-used frequently. Does that make sense?
I’m sure a lot of the irrigation components could be reused, though I bet you’d have to find a contractor willing to do it, which might be hard.
It’s true that you can’t resell a shrub easily, though I think there might be a limited market for trees. It might be easier to just take an inventory of the existing plants and leave them in place if you can (which is actually done reasonably often) or move them to a more appropriate spot (done less often, I think). If you can’t leave a tree or shrub, you can always request that the contractor put it through a chipper and use it as mulch or compost.
I guess there also needs to be some sort of system that lists or sells resusable materials. Otherwise no one is likely to know these materials are out there, unless they make a major effort. Here in Boise there’s a place that salvages old building materials and resells them.
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