For ethics, it’s the negative feelings that matter. But determining whether an organism feels anything at all (the other-minds problem) is hard enough without trying to speculate about whether there exit species that can only feel neutral (“unvalenced”) feelings. (I doubt that +/-/= feelings evolved separately, although their valence-weighting is no doubt functionally dissociable, as in the Melzack/Wall gate-control theory of pain.)

The word “sense” in English is ambiguous, because it can mean both felt sensing and unfelt “sensing,” as in an electronic device like a sensor, or a mechanical one, like a thermometer or a thermostat, or even a biological sensor, like an in-vitro retinal cone cell, which, like photosensitive film, senses and reacts to light, but does not feel a thing (though the brain it connects to might).

To the best of our knowledge so far, the phototropisms, thermotropisms and hydrotropisms of plants, even the ones that can be modulated by their history, are all like that too: sensing and reacting without feeling, as in homeostatic systems or servomechanisms.

Feel/feeling/felt would be fine for replacing all the ambiguous s-words (sense, sensor, sensation…) and dispelling their ambiguities. 

(Although “feeling” is somewhat biased toward emotion (i.e., +/- “feelings”), it is the right descriptor for neutral feelings too, like warmth,  movement, or touch, which only become +/- at extreme intensities.) 

The only thing the f-words lack is a generic noun for “having the capacity too feel” as a counterpart for the noun sentience itself (and its referent). (As usual, German has a candidate: Gefühlsfähigkeit.)

And all this, without having to use the weasel-word “conscious/consciousness,” for which the f-words are a healthy antidote, to keep us honest, and coherent…

That plants do feel is about as improbable as it is that animals (including humans) do not feel. (The only real uncertainty is about the very lowest invertebrates and microbes, at the juncture with plants, and evidence suggests that the capacity to feel depends on having a nervous system, and the behavioral capacities the nervous system produces.)

Because animals feel, it is unethical (in fact, monstrous) to harm them, when we have a choice. We don’t need to eat animals to survive and be healthy, so there we have a choice.

Plants almost certainly do not feel, but even if they did feel, we would have no choice but to eat them (until we can synthesize them) because otherwise we die.