I love Animal Crossing and the expansion to that game looks amazing, so that alone makes this $50 a year price seem reasonable to me. Heck, I'd buy the expansion for $50. And yeah, I know what people will ask, "What about next year? Do you wanna keep paying to rent that expansion?" The reality is, if they do this with Animal Crossing, what makes you think they won't do it with other games? For all we know, this could be their game plan going forward: Have expansions for major games come bundled with NSO premium model. Who knows? Nintendo likes to experiment with things.
Regarding the N64 + Genesis games, are those two platforms with the current offerings enough to get me to pay the extra $30 a year? For that, I'd have to go through the list of games for sure coming day to NSO with them. Of the ones coming, Banjo Kazooie, Paper Mario, Yoshi's Story, Starfox 64, and Pokemon Snap are absolutely games I will play. I'll probably at least try Sonic 2 and Castlevania Bloodlines. Now that I have a way to play Zelda MM without throwing my TV out of the window because of the stupid reset mechanic by using the suspension of software feature I will also play that game. So, let's just assume all of these games could be bought for $7.99 on a virtual console (and they'd probably sell for more than that if available that way), that's 8 games x $8 = $64. So, for me, in the first year, I will be spending $30 extra dollars on a collection of games worth at least $64. So for one year? This is a STEAL for me, especially considering Animal Crossing. Then you throw in the fact that plenty of other games will be added in time like they did for NES/SNES NSO and it makes it even better. And SNES wasn't at launch with NSO, so I also believe there could be another platform added (maybe GB/GBA) to this tier for free just like SNES was added for free to tier 1.
It all comes down to libraries. This combined library is of a greater value to me than the cost I will put into it, therefore it is a great price point. They'd have to charge like $100 a year before I'd get close to breaking even (especially if you add in NES/SNES games). Do the math on the games you'd want to play with the convenience of a portable device that has suspension of software feature. If you could save money playing the games this way, rather than buying, then this is worth $30 extra a year, if you could save money by just buying them on older platforms and don't care about modern features, then this may not be worth it to you. It's absolutely worth it to me.