We have been weighing up this same question khayman. IMHO, I would think it would increase the resale value. If a prospective buyer sees it is already legal height underneath, then they can easily build in the extra rooms. But saying that, for us, it might not increase the value of the property by more than we would spend on making it legal height ..i.e roughly 50k I think we will just leave ours as it is, level the old concrete slab, and make it an entertainment area with bathroom and laundry, and perhaps a couple of "utility" rooms