Thats another poison counter on each opponent, or more experience/energy for you
Regardless, I dont know that now is the time for more than 60 cards, but I do know that as the card pool expands, it gets easier and easier to find more spells of a similar power level, but no other lands are close to the power level of fetchlands, so the incentives to build to maximize the power of our lands over the power of our spells do increase in some way over time, which is to say that, even if its not right now, it could be someday, and getting there first might be the best way to truly break Modern.
This means you can save multiple versions of a card and revisit them later
You open your booster pack and look at all the cards inside (probably starting with the rare if you are like most people)
Even though Niv-Mizzet, Parun is the best version yet, I dont think the combo was close to being close for Modern
Its a drawback that needs to be considered when playing this mechanic