I wouldn't say Wizard City has an inspiration and if it does than it defiantly is not 18th to 19th century America. In America the mid 18th to the early 19th century was notably the golden age for the wild west/cow boy. If were Wizard City's inspiration than it would look more like the world of Cool Ranch from Pirate101.
It's more likely that the city that sprung up around the Ravenwood Academy of Magical Arts. Wizards have to buy school supplies somewhere, why not open a kinda of magical supply shop near the campus? Add to this that the diversity in the students ranges from at least Marleybone to Avalon (Penny Dreadful is from Marleybone and we know several major characters there are from Avalon. Not to mention the Drakes came from Dragonspyre). I think Wizard City is just meant to be some giant magical melting pot.
Krokotopia, I would say is almost exclusively Egypt.
Marleybone is Victorian England.
Mooshu is Japan, not China. For the reason that Mooshu has Samoorai and ninja pigs their real life counterparts being samurai and (human) ninjas which historically were only in Japan. China never really developed these kinds of specialized warriors/assassins.
Dragonspyre, if we exclude the accents, is probably the western half of Roman Empire after its fall.
Celestia is pretty much Atlantis, again another fallen civilization that was apparently inhabited by some alien species.
Zafaria is Africa.
Avalon is well Avalon, a legendary island from Arthurian mythology
Azteca is Mexico around the fall of the Aztec Empire.
Khrysalis is really tricky, I think it's also kinda like Wizard City with no known/designated inspiration.
Polaris is France around the time of the French Revolution.
Mirage is Middle East after the fall of the Persian Empire, fairly sure.