San Francisco: Was Wild West and Rice-A-Roni. Now it’s fabulous.
Singapore: Was an Asian Mos Eisley, now it’s an Asian Il Duce.
China: Was a quaint, backward and much abused giant. Now all your base are belong to us.
On the other hand, as far as I can tell New Jersey is still New Jersey, only more so.
Australia.
Was a punishment, now a reward.
Pittsburgh: Was a horribly polluted city of steel mills. Now it’s quite lovely.
Marseille, France: Notorious for its crime and corruption. Now it’s a great town with many interesting things to do and see . . . plus a beautiful harbor.
Ah, yes, the Garden State.
I was a little surprised when I saw Airplane! for the Xth time and realized they were making Detroit jokes thirty years ago.
On the subject of the OP, the IDEA of Japan hasn’t changed, but the conception of what comes out of it, production-wise, certainly has. Does that count?
Ireland. Once seen as a poor backward country, is now a country with one of the highest standards of living on earth, an information based economy, with a GDP per capita higher than the US.
Ireland: still seen as a poor backward country, in my experience 
There’s an increasing awareness that Ireland’s success is built on shaky foundations, with an economy in double-dip recession and vast numbers of workers leaving for overseas (50% of foreign workers who arrived in 2004 have now left).
The Irish economy is now seen as one of the poorest in Europe.
I think the perception of Germany has changed somewhat, over the decades.
In the 18th and early 19th century, the French were the most feared warrior nation in the world.
Not any more.
In Europe and America maybe. But the French have a reputation elsewhere of killing everybody who annoys them and all their male relatives to be sure.
The French under Louis XV and XVI were a “warrior nation”? 
Agressive under some rulers, victorious at times, but maybe I’m having a problem with definitions. To me “warrior nation” involves a culture that views war as a wonderful thing to do, an end in itself, and warriors (not to be confused with soldiers) as the ultimate vocation. Your mileage evidently varies, RealityChuck, but it seems as if you’d call any of the European countries of the time “a warrior nation”.
New York City in the late 70s had a reputation as decaying, crime-ridden hellhole teetering on the verge of bankruptcy. I’d say that’s largely changed. (Most people would still say that NYC has quite a lot of crime, but it’s probably not the first thing to leap into your head when the city gets mentioned these days.)
I suppose it depends upon which continent you were living on at the time. “Whatever happens we have got / The Maxim Gun, and they have not”
Many Mexican border towns, places like Nuevo Laredo, Juarez, Reynosa, Matamoras, etc used to be a great place to shop for the day, get a good meal, load up on cheap bottles of tequila and the like. They were thriving places where the people were friendly, it was fun to barter and you felt reasonably safe. No mas.
I was specifically going to say the Brooklyn neighborhood of Bedford-Stuyvesant.
Then: going there is synonymous with insanity (as memorialized in the Billy Joel song “You May Be Right (I May Be Crazy)” I walked through Bedford-Stuy alone…)
Now: rapidly gentrifying brownstone neighborhood with tons of upside for the savvy real estate buyer.
Most people would be wrong. NYC is the safest large city in America. Minneapolis, for example, has about 10x the forcible rape rate. (1.08 per 100,000 vs. 0.1 per 100,000) and about double the overall violent crime per capita (11.4 per 100,000, vs. 5.5 per 100,000).
Pretty much any place where some notable historical event happened. For one example, Peenemünde used to be regarded as a remote but pleasant vacation spot for wealthy Germans; now it is associated with V-weapon production from WWII.
And Dachau used to be an artist’s colony and spa resort.
Russia.
Then: scary evil empire trying to take over the world.
Now: wild-west klepto-plutocracy not trying to take over the world.
Of course, both characterizations did not necessarily contain all the facts.
And the stereotype of Japanese men has gone from fanatical warriors to metrosexuals.
Well, Mars used to have water, and canals, and Martians. Not so much now.