Should you re-do a crawl space at the time the end of the house is knocked down?

The house has a crawl space. It is nasty and wet. It needs to be redone, like preparing a gravel trench/drainage pipe/etc. One possibility is just to do it. Another possibility is to wait until an addition is made to the house. The end of the house is a poorly designed bedroom with a separate roof from the rest of the house. I want to tear down that room, add 2 rooms, closets, and a garage. I was thinking of tearing down that one room then have much better access to the crawl space, do the crawl space work, then build the addition and a concrete slab for a garage. Is that the best order (to access the crawl space when the addition is done)? For bidding purposes, contractors seem to like to bid on new work and not mix crawl space remodelling with new additions, but I could be wrong.