I know that very often, when Cloud is mentioned, money and spending is brought up. I feel like it's pretty obvious that there is money sent either way to get a character in a game like Smash. There may be some people who don't think Cloud was worth it, but I would have to disagree.
I probably seem like a Cloud fanboy, but it's simply epic that he's in Smash. The All-Star lineup of Gaming (not just Nintendo) All-Stars in Smash is unheard of. No other series has ever had a cast like Smash Wii U/3DS. It's incredible to think you can match up some of the biggest icons in the same game.
I think whatever cost to get Cloud in Smash was worth it. I don't have a degree in economics to know for sure...I also don't know the details of it. I do realize Final Fantasy VII is considered one of the greatest games of all time, and costs regarding the game can be high. There's a reason for that.
However, no matter what the deal cost Nintendo, we got:
Cloud
Two costumes (one from Advent Children, the movie)
Midgar Stage, with stage hazards
Midgar Stage (Final Destination version)
Let the Battles Begin! (one of the most iconic music tracks in gaming)
Fight on! (Boss theme from FFVII)
A unique victory theme for Cloud (it plays even after the usual jingle, loops)
Art Piece for Smash Wii U/3DS website, crafted by Final Fantasy artist Tetsuya Nomura (famous for his work)
Now, with the battle theme being one of the most iconic music pieces in gaming, that couldn't have been cheap to use. Now imagine wanting One Winged Angel, a track that is considered one of the best pieces in gaming history. That certainly wouldn't be cheap!
Basically, Cloud returning depends on money. Yes, there are diminishing returns on guest characters. But for a game like Smash? I don't know that we're there yet. If they retain Sonic, Mega Man, Pac-Man, Ryu, Cloud, and Bayonetta, it will be one of the greatest rosters of all time. Hands down.