I can't find a simple historical total return index on a free source but here's a calculator[1]. It says to me that 100% dividend reinvestment in the nikkei since 1974 would give you a total return annualised at 3.2% in yen and about 3.6% in dollars. Most people would have significantly better hurdle rates than that. So investing in the nikkei if you're a yen or dollar investor has been pretty average over the long term no matter how you slice it.

[1] https://dqydj.com/nikkei-return-calculator-dividend-reinvest...