I have to disagree with @what. While it's true that nobles are born and raised with many advantages ON THE AVERAGE, there is still a large fluctuation about the mean. And a stupid noble will often not be more successful and happier than a stupid ditch digger, for the obvious reason that the stupid noble is out of place, forced to attempt to perform at a level he cannot possibly achieve. His stupidity ruins the lives of all those beneath him, who were counting on him to properly perform his societal duties.
Similar arguments could be made for aristocrats who are evil, lazy, arrogant, sickly, crazy, foolish, profligate, or any one of another dozen human failings I could name. (Or combination thereof!)
This is one of the main reasons that Americans rejected aristocracies. It is also, by the way, the reason why American voters ought to be highly skeptical of politicians following in their parents' or spouses' footsteps. (Personally, I would make that unconstitutional.)
What does this off-topic rant have to do with your question? :-D The upper classes in your book(s) should have all the normal problems of the average Joe, but those problems will get addressed differently than those of the average Joe. Remember the movie, "The King's Speech"? For an average Joe, being a severe stutterer would have been an annoying handicap. For the heir to the throne, it was cataclysmic.
So, upper classes are EXPECTED to use hoity-toity words, whether or not they have the intelligence or wit or vocabulary to pull it off properly. If they DON'T use hoity-toity words, it is covered up, or chalked up to quirkiness, or made fun of by superiors (to their face) and by inferiors (behind their backs). Exception: if they are powerful enough, their manner of speaking becomes the new hoity-toity. (Case in point: one English king had a lisp. Soon all the aristocrats were affecting a lisp, and eventually speaking with a lisp became a sign of aristocracy.)
Your upper classes are EXPECTED to converse "intelligently" about "proper" subjects, but they won't necessarily be told how stupid, trite, and plain wrong their conversation is. Use this; run with it; have fun with it; be cruel with it; make it a source of pathos. Have some of your aristocrats be the genuine article, of course, and have them react in different ways to the pathetic aristocrats who can't keep up. See "The Scarlet Pimpernel", "Zorro", P.G. Wodehouse's Jeeves novels, Jane Austen's novels, and most of Dickens's novels.
For ten-dollar words, use a Roget's Thesaurus. (NOT a "New Roget's Thesaurus", which is awful.)