Of course: If it is not properly prepared or not prepared the way it was ordered. I will send back something if it is overcooked, burned, undercooked or something is spoiled. I will also send back meats, in a high end restaurant (i.e. Morton's) if they are tough, sinewy or over seasoned.
I have worked in high end restaurants and have close friends who are chef/owners of restaurants and one who is a VP of the Culinary Institute of America. I know what is cooked well and what is not. I also know the difference between something tasting "off" and something I don't like. If I order something and the spice combination or flavor profile is not to my liking I may just try it and just say "Well, I guess I won't order that again." If I am offered a replacement then I may take them up on it but I will not force the issue.
A cruise ship is different. If you don't like the taste of your dish you can just ask for something else. These dishes are not prepared "Ala-minute" they are set up in groups and the waiter just needs to go and get another.
The truth about sending something back and the cook will do "something" unsanitary to it is so overblown that it is ridiculous. It is like the story about someone finding a rat in their Kentucky Fried Chicken. Did it happen? Probably, but now just about every city has the story of someone finding a rat in their chicken at the KFC on Whatever Street. Has someone spit in the hamburger that someone sent back? Probably, but the chance of it happening are about the same as you getting in a car accident today.
Any decent, high end, restaurant would never dream of doing something unsanitary to the food just because it was sent back. If you keep sending something back that is properly prepared you may get told off but your food isn't going to be spat in or rubbed on the sole of the cook's shoe. I know when I was cooking back in "the day" if I or any other cook had done that they would have been fired but not before the Sous or Exec Chef had an accident with the fryer and you were the victim.
I have told and I have seen the Head Chef tell someone to leave the restaurant when they have sent back orders and replacements that were perfectly fine. Yes: restaurants have "black lists".
A true professional does take it personal if they send out something that isn't right. However they want to show you that they can make it right.
The one exception is when someone orders a "Well Done" steak or other meat. I've seen some pretty bad "burnt offerings" come out when this happens. Especially when a truly well done steak is sent back because it is too rare.
(Watch out Kuki)
Now: In fast food restaurants or somewhere like "Denny's" or anywhere that the head man in the kitchen could easily have been working at the Jiffy Lube last week then your chances are greater that they "might" do something but they are still remote.
The best advice I can give anyone is: If it isn't right send it back. The Chef will appreciate it because he would much rather have you happy and telling everyone what a great meal you had rather than leaving unhappy and telling everyone how bad it was.
Paul: I would have your wife make sure to tell the waitress, when you order, that she wants the food piping hot and if it isn't she will send it back. It will lower the chances of her having to send it back and keep the waitperson on their toes because, in most instances, if the food is cold it is the waitperson's fault. They didn't pickup on time.