Why a flash cart when emulation and other things can achieve so much more? Frame boosts, textures, resolution boosts, all the perks of emulation in general. For some things that is a smaller sell but the N64 has aged like milk in many cases -- I really can't play much original N64 stuff today on hardware, give me the nice ports to later generations and I am nice and happy (Perfect Dark is a slideshow, XBLA Perfect Dark holds up today in many ways, Rare collection on the xbone is also good stuff and most of that appeared on other things), Mario 64... eh but the nice source recreation does very nice things, and on the emulation front then retexturing, hd textures, someone fiddling with models, draw distance, frame boosts, widescreen and more have been features of emulators for many years now.
If you buy a flash cart then you are also almost compelled to consider something like a RGB mod or other nice video out, not to mention working controllers is a trickier hobby (though fixes do exist nowadays), and I hope you have a memory expansion too.
