We drew nudes in order to learn how to 'see' and recreate the human form..not to just look at a nekid person!
I remember being pretty excited because the one woman I thought I'd NEVER get to see naked volunteered for figure drawing class.
I think a lot of us guys were pretty enthusiastic about the idea, and at the time I am not sure if I'd ever seen a naked woman in person before, let alone *this* particular naked woman.
Yeah. It was pretty disappointing ... context.
But in this particular image, if the model were nude it would have just been silly IMO, and yes, it would have been sexual. Whether or not that is offensive to you, well, that's kind of your call to make.
But honestly, I don't think it'd necessarily be any *more* sexual and silly than it already is - and it is already a kind of silly photo. Perhaps it'd be a little less silly if she were nude, as it is now a woman posing in a mildly sexy way (*not pornographic*, but yes, this is a somewhat provocative pose) on an irrigation pipe wearing a sweater is kind of silly - at least if she were naked then it'd be more sexy. Though, once I got over the naked boobies (and I do like naked boobies), I'd probably be wondering what the heck is she doing on an irrigation pipe, naked? But so what! Naked Boobies!
Ok. I'm not trying to be offensive here to the OP's lovely wife (though i probably am), but rather, I'm making a point. If this image can only work if she were nude, then it's relying on the provocative nature of an attractive person in a mildly sexual pose *being* naked. It's relying on the viewers sexuality, rather than the photographer's artistic insight. There no dialogue, aside from what you'd expect from a group of thirteen year old boys looking at a playboy!
In my opinion, that is sort of what defines pornography, it is solely about the sexual/sensual/erotic/whatever nature of the model and nothing else. I've seen many of images that is shot and lit well, but the only reason I'm looking at them for more than a few seconds is because the model is naked - and yeah, I like looking at naked women.
If she were dressed, it may as well have been any other well-executed portrait. If the only thing that separates an image from any other is the nakedness, then it's not an "art nude" - it's just porn/erotica. I'm not sure that there is anything wrong with that, but it is what it is and you have to be aware of this when you're working with these subjects. To create a genuine "art nude" is probably the most challenging assignment you could give yourself. Simply adding a fig leaf here or a whip of hair there in strategic places won't suffice.
Otherwise, just admit it's porn/erotica and get over yourself. And for god's sake, don't call people prudes because you're too shy, pompous or self-righteous to admit it!