The cartridges may one day become collectors' items. They've already been phased out of most used game stores.
So Should I Get One?
To be blunt, there's no practical reason to spend hard were transported onto better systems. The kitsch factor for the N64 is off the charts, though. If you're into antiquing and want to drop a few bucks on a silly slice of retro gauche, you could do worse.
Do check out the Xbox 360 game consoles).