i say get the first mario party as well, just so you have the trilogy. I havnt played my copy in like 13 years or so but its just nice to own all three of them.
If it was like a $5 game, I probably would. But I'm currently fixing all 4 of my controllers (controller #3 is up next!) in preparation for Mario Party Down (
http://www.youtube.com/watch?v=Kxk06CcF-hY) in a month or two with some friends I haven't seen in awhile. Mario Party 1 is pretty much the bane of an N64 controller. I can't watch my babies be destroyed again.
Mortal Kombat Trilogy causes non stop battles here at college 
I don't know, I'd hardly call it essential. The Playstation version is superior unless you really, really hate loading.
Apple you have captured the essence of what I am looking for. I have a PS2/3 (both backwards compatible), an Xbox 360, a Wii, and an N64. I'm looking for games that aren't easily outdone by other remakes or updated versions. And I don't want to buy virtual console games.