Are there any definite no-nos? *I know that chocolate is bad for dogs,

If the dog is happy and thriving on the regular kibble, that's an
excellent place to stop. If the dog is eating well without being
fussy, then boredom isn't an issue. Don't be too tempted to read
human motivations into your pet.

If you still cannot stop your wife from feeding leftovers, there are
several other "gotchas" besides chocolate. Onions and Garlic are bad,
and anything related (scallions, leeks), as are grapes and raisins
(sultanas if you're in the UK). Every dog is different, and some of
these build up over time, so just because you've gotten away with
feeding something once or twice with no obvious effects doesn't mean
it is safe, or because "it's only a little bit".

I've always been told by my vets not to feed table scraps, as I recall
it was mostly because of the high fat and the salt content--there is
usally way too much salt in prepared human food for a dog, which could
cause or aggravate kidney issues.

Hope that helps,
--Glenn Lyford