A few things going on here that you need to evaluate. First, finding a qualified appraisal consultant for the property. At first blush I would expect a cost to be between $2500-$5000 for a cursory appraisal of a project of this size. Then you evaluate the value of the appraisal to your decision as to expected market value with a sell/hold threshold.
The attorney that offers the opinion on the speculative value as “nothing valuable” is way outside of their field of expertise unless they specifically practice in this area and have a supporting appraisal. So, beware of the intention.