How much would you pay for a character, stage, item, piece of music? Would you refuse to buy anything if it came to it?
Personally I find it a lot easier to quantify value if it's a package deal, if it's just one item I'd feel more uncomfortable about it. I guess it's more obvious that I'm being fleeced.
Considering you can buy Smash Bros 4 3DS at around €44-€49, with an initial roster of 44-50 (probably) along with countless stages, music, game modes and other things like trophies. I'd feel hard pressed to pay much for any one particular feature. That's why I prefer expansion packs to dlc, there's usually way more bang for your buck.
Even if you paid €1 for a new character it's still disproportionate to what you originally paid for the game. If you put a value of €1 on every existing playable character you'd already reach the full cost of the game before even considering existing stages, game modes, alternate costumes, remastered music, bosses, and items.