Of course, you shouldn't rely on continues. Even though you can use them, you should certainly try to get by without them. Sakurai seems to feel the same way, which is why you get punished for using continues in Super Smash Bros. Brawl.
Not that the punishment is all that bad -- Kirby won't puff into your home and slap you in the face, for example. Yet, in Classic Mode, each continue comes at the cost of points and coins. Your score will automatically get cut in half, and the amount of coins you owe is based on the difficulty you're playing in. Naturally, easy playthroughs cost less coins than difficult playthroughs. And yes, these are the same coins that you'll be using in Spectator Mode. Just like an arcade game, if you don't have enough coinage to continue, it's game over.
As for Adventure Mode, the consequences aren't as bad. You don't have to spend your coins to continue, but you'll lose half of the trophies and stickers that you've collected on your current quest. You'll also receive less coins when you beat stages after continuing.
We wonder just how hard these single player modes are going to be. Until we figure that out, you can bet that we'll be big penny pinchers.