I consider it to be perfectly fine, if used correctly. There are many great examples. Lets take the Fab Four.
"In my life" is a stunning piece of writing, lyrically, melodically and chord structure...ly
And, in the middle there is the lovely double time "fake harpsichord" solo, created by recording a piano at half speed and then doubling the tape speed. This sound is both ONLY heard in the break, and an odd sound in general.
The ear loves it. It is a fresh sound, and, a BREAK! Geddit?
Now, of course, you have to avoid gimmickry for it's own sake. But, I have never worried about a sound ONLY appearing in the break in an arrangement and have used it myself.
On "Stay in Touch" I bring a piano in during the break, nowhere else. In my conspiracy comp entry "Disposable" in cometh an electric guitar solo.
The arrangement you speak of, and the method of keeping it "in" thereafter is somewhat aligned with live performance. Of course, having a harpsichord player on stage for four bars of a song would be silly. So they add subtle noodles elsewhere. If they aren't required, if they don't add to the arrangement you are recording, then don't worry! Of course, now with synths/samples on keys, such whimsy is a lot easier to employ!
Lastly, the market, the listener, doesn't think like a musician. They hear music, not arrangements. They don't think like a muso, concerning themselves on the frivolity of a four bar sax that sods off right after. They just enjoy the part played
