(Apologies in advance for this post being somewhat technical and jargon filled post - I have not yet found a way to make lomdish concepts intelligable in pure English in a succinct way.)
Getting back to the hana’ah questions from Monday that I left hanging, the issue of mishloach manos seems to be the easier one of the two questions raised. I don’t think one should reject the P.T. out of hand because hana’ah is not food – after all, according to some you are yotzei if the mekabeil is moichel and gets nothing! The simplest answer seems to me to be that mishloach manos requires a shiur of something chashuv, as well as 2 distinct items, and the shiur here is lacking. But there maybe more to it – see below.
As far as why hana'ah of having a token gift accepted is sufficient for kinyan sudar but works in the case of kiddushin only where the one accepting the gift is an adam chashuv, David commented, “In the case of chalipin, the hana'a itself does not effectuate the kinyan. The hana'a is needed only to provide the "gemirus da'as" on the part of the makneh to transfer ownership over the object. It stands to reason that even a limited degree of hana'a suffices for this, and therefore even if the koneh is not an adam chashuv, his receiving the gift suffices to establish the makneh's gemirus da'as. In the case of kiddushin, the hana'a itself effectuates the kinyan kiddushin (am I correct?), and perhaps a higher standard of hana'a is required.” I was not sure what he meant by the hana’ah “effectuating the kinyan” in the case of kiddushin, but I am guessing he is driving at a siman/sibah split – by the case of kinyan sudar, hana’ah is just a siman, an indicator, that consent to the deal has been reached. By kiddushin, it is the sibah, the transfer of the ring or hana’ah is the actual cause of the kinyan being closed. To use an inexact analogy, hana’ah is like kinyan kesef; payment for an item is not just a means to indicate your consent to a sale, but is the very vehicle through which the sale occurs. (Whether hana’ah by adam chashuv is a form of kiddushei kesef or a new type of kinyan is an open question, see Rashba, Shiurei R’ Baruch Ber.)
My first impression was to try to distinguish between da’as makneh in the world of kinyanim and the da’as required for kiddushin, which may demand a hight standard. Recall that one can retract from a kinyan in toch k’dei dibbur, but consent to kiddushin is final. Rashi (Kiddushin 3) explains that chalipin is an invalid form of kiddushin precisely because it does not effect the required da’as makneh on the part of the woman, but we know that it clearly does in the case of monetary kinyanim. This approach is a bit hard to digest because other Rishonim (e.g. see Ran Nedarim 30) indicate that the woman does not even require full da’as makneh by kiddushin but passive consent suffices (see Shiurei R’ Shimon Shkop).
After mulling it over some more, it seems to me that a sharper bit of lomdus is in order here. While both kinyan sudar and kiddushin require some form of da’as makneh, kiddushin has the additional requirement of there being a mekadesh, a ba’al, to create the kiddushin. Regular hana’ah is enough when da’as makneh alone is sufficient, but the hana’ah merubah (as the Rashba calls it) of adam chashuv is needed to create a "din ba’al" on the mekadesh. Returning to the mishloach manos case, I would apply the same logic (and David started down this road as well) – it is not enough to get food, but there has to be a meshalaich from whom it is sent (though see our past discussion of that issue here). Hana’ah which occurs m’meila is insufficient to create such a chalos.
Is this enough to solve the original question of the apparent contradiction in R' Zeira's view which was the springboard of this discussion? Maybe I'll fill in the details later...