Bad question. Try this: it's neither the duration nor the season that truly determine the value of a trip, but rather the flexibility and alignment with an authentic cultural experience.
Here in Japan, even a short stay can be incredibly rich if you aim for local events or cherry blossoms, regardless of the season.
What matters is not to minimize costs at all costs, but to maximize the cultural value of every yen spent.
A well-planned one-week trip, even during peak season for a specific festival, can surpass a month of low season wandering aimlessly, relying on alternative accommodations or simple meals.