A code to unlock all options is a really good idea, and it's something that Puyo Puyo games (even the recent ones like Puyo Puyo Tetris) did. Champions didn't have since everything was already unlocked from the get go so it wasn't necessary (but it has codes for 1P CPU and super-difficult AI).
Lost levels is hard, but it's its difficulty that makes it fun. Could just be me, but i love difficulty in games, hence why the challenges in nsmbu are some of the most fun i've ever had in a mario game
anyway to share my unpopular opinion, i don't like bikes in mario kart. I always go with karts and sometimes atvs in mk8 but i tend to avoid using bikes.
i'd love to finish the lost levels but it's so damn hard i just can't. i mean if i used save states i technically could eventually but that would take AGES and i don't have that much time. plus a lot of the difficulty comes from dated physics which makes it a bit frustrating
I try not to use save states, but I end up getting so frustrated with the game that I just have to use them. I use them in NES games mostly, and I try to avoid using them in other games unless it's for saving the game progress until I continue playing.
whilst both extremely high and extremely low difficulty tend to lower my opinion of a game, if it's a game that's generally somewhat easy vs one that's generally somewhat hard i'll generally pick the easy one. example would be galaxy 2 vs sunshine, even though sunshine isn't extremely hard i still find it a bit offputting whereas galaxy 2 though i do find it generally a bit easy at least for any% it's generally more enjoyable than being too hard. galaxy 1 is pushing it a bit more but i still love that game nontheless too.
If a game gets unfair and cheap, "cheating" becomes a justified course of action. Savestates also provide a quick way to experiment with the game without breaking anything.
And at the end of the day, you have the option to either use them or not. You wanna play with savestates? Do it. You don't want it? Then don't, all it takes is not pressing the button. It doesn't hurt anyone to use them.