I always thought owning both the .COM + .NET increased the value of the .COM. Guess that was a misconception, doesn't seem to be that simple!
there are so many aspects of domaining, which are presented to the masses in generalities.
so much so, that it (domain valuation) can be conceived as simple process of attaching value down and across extensions.
the .com probably would have more value in the eyes of the .net owner, if not the same person
however, if one person owned both, their combined upsell value could be determined by a party interested in acquiring both extensions, and or plus the owners assessed value of that combination should they decide to sell.
that value could also be determined by traffic and revenue, along with number of previous inquires to purchase.
but if there is only interest in the .com, then what value does .net have to the potential or to the owner?
that could depend on the keyword/category
there so many different scenerios one could paint to illustrate which way value will lean, and how it will/can be perceived.
imo...