I finally got a Nintendo 64 and a copy of Ocarina of Time in 1999 a year after OoT was released, and felt like acquiring the console was justified from that one game alone. So yes, I'd say it's worth picking up a Nintendo 64 for Ocarina of Time and Majora's Mask. Ocarina of Time is basically Link to the Past in 3d and I have a tough time deciding which one is the pinnacle of the series.
GameCube's are extremely cheap. I think I paid $20 for a third one less then a year ago and $10 or so for a Game Boy Player from GS to make one a dedicated Game Boy Player so I didn't always have to change disc and controllers on my original everytime I want to play a GBA game (I play GC games on my original and keep a second GC NIB for the day it may be needed).
I wouldn't spend more then $20-$30 on a used GameCube in good condition with a controller, power supply, and first party controller.
The GameCube Zelda's are fun too, but never quite rival the two titles on the N64. Even still, Wind Waker and Twilight Princess are great games and Four Swords Adventures is an interesting experience that modernizes the graphics from Link to the Past and brings level based multiplayer gaming to the Zelda franchise.
There are also two compilations on the GameCube. One includes Ocarina of Time and an interesting hack of it that supposedly recycles much of the content that the unreleased Ura Zelda project for the N64 DD was supposed to be (Think of it as a second quest for Ocarina of Time).
Then there's a second compilation with both NES and both N64 titles (No Link to the Past as Nintendo had just then released it on the GBA). It's a nice collection, but be aware that there are issues with Majora's Mask including a slower frame rate, crashes, and the loss of saves. And neither N64 Zelda ever feels quite right with a GameCube controller in my opinion.