Yeah, Double Dash was very similar to Mario Kart 64 but just did everything a lot more fancily. Most of the maps were even based on Mario Kart 64 maps, which made for some nice nostalgia.
In fact, nostalgia is another huge factor of Mario Kart for me. It's awesome playing a game absolutely packed with things that take me back to being about 8 years old, but refined; the fact that classic maps are included takes it even further. Some people might see that as boring and lacking inspiration, but I guess you have to enjoy Nintendo games in general to understand (seeing as most are series that've been running for well over 15 years).
It's kind of like how James Bond reused the same elements time after time, but you grew to enjoy that familiarity and convention and thus didn't mind. But of course you wouldn't want every film maker to do it.