Role of food as an allowed monastic luxury
Actually, high beds and seats are not disallowed; making them is. It's not really so cut and dried, and the Buddha seems to have allowed for the fact that (some) luxury is not the problem; attachment is.


  throwing a feast or banquet is actually encouraged as a means of merit making for the lay follower? 


Not in the texts, it isn't. It is actually stated rather simply as "refined food both hard and soft". If anything, the point is to make mention of the rich people putting care and sincerity into their gift, which is very important for cultivating wholesome mind states.


  Especially when one considers how this sets apart the poor lay follower who can only afford to feed the occasional monk on his alms rounds.


The texts often make mention of the greatness of poor people giving coarse fare according to or beyond their means. The important point is one's quality of mind.


  who in their right mind could think they could honor the Buddha with a feast? If anything, he probably favored the simple flavors of fruits of the forest over puddings and rich food.


Not according to the Buddha; he was raised as a prince and his palate was quite refined; when he first went on alms as a bodhisatta, he said that it felt like his stomach was going to come out of his throat in protest of the coarse fare. I think it is unfair, though, to suggest that the Buddha favoured any type of fare. He did praise a monk who  separated his food into wholesome and unwholesome once, though, so there is that.