Japan's snowfall is concentrated midwinter. Locals say March in Japan is like April in North America. So late spring in Japan is good only for backcountry touring to the high Japan Alps above lift service or on Mt. Fuji.
For pure ski quality the Alps in May/June are no better than the late places here like A-Basin, Snowbird, Whistler, Bachelor and Mammoth. Most May/June skiing in the Northern Hemisphere should be viewed as an adjunct to other tourism IMHO.
To some degree this applies to the Southern Hemisphere trips in August/September also, due to erratic snowfall ski conditions and the expense of traveling that far. All 7 of my Southern trips have been roughly half skiing, half other activities.
In terms of lift served terrain quality Las Lenas is in a class by itself in the Southern Hemisphere, reminded me some of Grands Montets at Chamonix. Everywhere else is more similar in scale to mid or smaller scale areas in North America. However the lift that serves 80% of Las Lenas runs only 40% of the time due to storms, wind exposure and not always competent management. But if you want the big mountain skiing, Las Lenas is where you should go, maybe for 2 weeks to increase the odds you get Marte open at least a few days.
With the exception of Bariloche, which has VERY unreliable snow, South American resorts are isolated in the mountains with not much to do on down days.
I wrote a feature on Chile's skiing within easy range of Santiago also:
That trip I combined with 9 days in Peru including hiking the Inca Trail. After that it was no problem sleeping/skiing at 9,400 feet in Portillo or 9,900 at Valle Nevado. After the Las Lenas trip we went to Iguazu Falls and Rio.
On the Chile trip I did not get to Chillan (6 hours south of Santiago), which probably gets the most snow of South America lift service.
New Zealand works easier for the "mixed vacations" combining with other activities. You are a staying in resort towns, not in the mountains, so there are lots of things to do on bad weather days, particularly in an adventure center like Queenstown. And on the way you can go to prime tropical destinations during their pleasant winter dry season like Fiji, Tahiti or Australia's Great Barrier Reef.
I collaborated on an overview of New Zealand skiing: http://www.firsttracksonline.com/2006/12/31/kia-ora-new-zealand/ and later wrote a more detailed report on some areas accessible from Christchurch, the main international gateway on South Island. http://www.firsttracksonline.com/2011/06/17/new-zealand-skiing-snowboarding-canterbury-hutt-olympus-broken-river-porters/