If the majority of SRG's value will be realized via renting existing and redeveloped/newly developed space, then I think incremental rents and the related return on capex are what will help us determine the intrinsic value of the company. Another important factor we must try to predict is the amount of capital they can invest on new and re-developments every year and in total over the next 10+ years with this portfolio.
On the other hand, if you believe SRG will begin to sell off significant portions of land, then market value and it's approximate relation to book value are of importance. Returns on capex do not matter if we are liquidating the portfolio. In the current state I don't think SRG plans to liquidate it's land portfolio and therefore book value is not of utmost importance.