Good to know–I think Innovation is a great game, so I’m glad to hear good experiences are possible with more than two!
You are right about the decks running out–good players will rarely get to the age 10 decks. (though finishing in age 6 is pretty darned good in my book!)
But still, because of the nature of the game–a whole bunch of cards that break game rules and generally allow you to mess with other players–things just get inherently messy at higher player counts. I know others (including Tom Vasel, one of the game’s champions) has claimed the same thing.
Now, having a great game that turns from strategic to rather more tactical by increasing the player count isn’t necessarily a bad thing–in fact, to quote the jackass usurping prince from Frozen, I love crazy! (…I have kids.)
But generally speaking, that can be a detriment in many people’s eyes, and it’s worth pointing out here.
Actually (and hopefully, constructively), that raises a good question: can games that change their nature/playstyle at different player counts be considered games that “scale well”?
Many examples of my favorite type of game (tactical skirmishes/crawls) play from 2 to 5–but the experience of playing changes notably with different numbers of people at the table.
The scenarios in Imperial Assault, for example, take a whole different difficulty as a two hero game, and tactics change considerably. Personally, I like the game at any player count, but I have a hard time saying it scales well–there are some notable bumps.
Massive Darkness, on the other hand, shifts player counts like a bicycle whose chain pops off every time you go below 3, and that nearly seizes up when you go above 4–so definitely not a game that scales well.