I don't count arcade titles.
Yeah the requirements for unlocking parts in MK7 is insane, MKDS is piece of cake, MKW a bit more difficult (never could reach 3 stars lol) and MK8 idk, I bought the Wii U with MK8 included since it's no longer console only....
I think it might be possible through save editing to get the golden parts, but as far I know you only can backup ghost data. (and if you like, sharing them with others! (which is not possible in an official way)
I agree that the last few titles are getting rubbish, MKW is literally the last good one imo even though they changed the mini turbo. Too bad online racing became shit thanks to hackers (idk how things are going through wiimmfi)
And you definitely either need a DS Lite or a phat for MKDS (imo DSI XL works too, but they are like "nope"), because you can then get consistent snaking. Amazingly my best record on rFS 3lap is done on my DSi XL which is hard to beat even when I try it on my phat, guess it's more like getting used to whatever handheld type you use