Bird, I'm curious regarding your "Complete concrete slab" comment. I would strongly recommend a good steel reinforced concrete footing/foundation and a similar stemwall (cast or grouted block) but don't see the justification for the extra expense of a complete slab under a raised floor.
It would not be a bad thing. In fact it would offer some benefits like not crawling in dirt to do things under the floor and simplified pest control, no mud under house in any wet period. But as far as structural integrity goes I don't see it as cost effective. Nice to have but not required. That's my take. I'd be pleased to hear your reasoning.
Pat