Hahaha, awesome!! Thank you so much for the help NYYRIKKI (and Lars)! 
I love this community.
There is, however, still one bug left at least that I discovered recently:
In the name entry screen, whenever you wrap the cursor around by pressing down when the cursor is at ヤメル/QUIT or START, the cursor starts to misbehave and it doesn't select things or move as it's supposed to.
As for Nyancle Racing's difficulty: For whatever reason the second course is by far the hardest of them all. It's almost impossible to finish without the upgrades. And if you die, you lose one of EACH upgrade, which is a brutal game design choice by devs. 
The trick to complete course 2 is to buy as many green fan upgrade as possible to get the most out of jump ramps, as well as using the break often mid-air, which forces you to land earlier (you can make the landing more instant by having enough engine upgrade).
Alright. I played a couple of sessions to completion of the newly fixed version. Indeed, the game-breaking bug has finally been fixed after 35 years! And the upgrade counters are showing correct values to boot! Thanks again, NYYRIKKI!