4. Voting. Each parcel of land benefited by a private road, private way or bridge represents one vote under this section; except that, if the bylaws of the association authorize more than one vote, then each parcel may represent no more than 2 votes under this subsection. The call to a meeting may state that an owner may elect to appoint another owner to vote in the owner's stead. Owners voting by absentee ballot must be polled on all voting items that were not included in the agenda and the final tally must be reported to the owners.

That is the language. You are right, an owner may only appoint another owner to vote in his stead.

Yes, the "may" language means that it is not required. It would be a by-law that would be put up for a vote. And on the question of whether the association may broaden the requirement for a proxy from "other owner" to spouse, it seems to me, that's the prerogative of the majority to do. I imagine the intent of limiting it to "other owners" was to prevent disgruntled members from causing some kind of disruption, perhaps broadening the attendance at the meeting to people in whose presence the membership would not want to conduct business -- not ever made clear, but something along those lines I imagine.