I can list 3 reasons why this restructure will add value to...

I can list 3 reasons why this restructure will add value to existing shareholders.
1) WRT, the newly formed retail property trust by WDC, as a matter of fact is exactly what large insitution and many Australian investors want, the supply of such quality property trust is tight. By spinning it off, WDC creates a less complex entity that is easier to value. As a result valuation for assets under WRT will be at a premium to what the current market valuation is. This in term will boost share price in WRT which is also in the interest of existing shareholders as they will be issued back WRT shares.
2) Due to empirical study, most shares reacts positively to spin off, the reason is probably it's easier for valution.
3) I know I kind of mixing SP with value in above poits, this point is to clarify from a DCF or NPV approach. In short, more transparent/simpler/less complex/smaller entity reduces the risk premium/buffer an investor demands, therefore the discount rate applies to all future cashflows should adjust downward, which in turn boost the net present value of those cashflows, or i.e. the value of the firm.
4) some assets may have potential extra values that need to unlocked by spin offs, i.e. some assets worth more in the hands other than WDC, for example, WRT may be able to put a better price tag on those spin-off assets. (this point is kind of summary of all above points in short.)

PS: I think the SP reaction after 2 days of trading halt will explian it all.