By 'silly tricks' of course I don't mean basic training, all of mine are taught to come when called,not to approach other dogs and to walk sensibly on a lead, they aren't expected to shake a paw, roll over, twirl around, dance on their legs etc just to get a biscuit or to entertain me. They get their stimulation in a way much more geared to a dogs instincts by being taken on two long off lead walks a day, they're dogs, they love being dog sand I love them being dogs.
Separation, exclusion and being denied freedom is punishment and that's what cages do, if I were to shut one of mine in a cage they'd wonder what the hell they'd done wrong!
All dogs need are boundaries and yes it may take a bit more effort to do it without locking them in a cage but in my opinion they are worth the effort.
If, for example, your dog goes mental and jumps up visitors you aren't teaching them the correct way to behave by shutting them away, if anything you are exascerbating the problem and will either wind them up even more or teach them that visitors are a bad thing and to them means being excluded for doing nothing wrong. They are pack animals and if you want a pet that is happy to spend a lot of time on it's own then get a cat.
For anyone interested in learning how the dogs mind works I thoroughly recommend the courses run by Shaun Ellis at the Wolf Centre in Coombe Martin, they'll help you understand dogs a million times better than any pet training course.