Clones to me aren't inherently bad. But they should make sense.
To be fair, all of them in Brawl... do make sense... except for Capt. Ganon. I know it was a must for Melee... but by Brawl, it's something that should have been addressed. But beside him, I don't really mind.
And for me, there is a "tier" list for Clones. They are Clones/Costume swaps, Clones as in Semi-Clones and unique characters.
Level 1 Clone - Wario & Warioware Wario, Mario & Dr. Mario in Project: M, Wii Fit Trainer and Mii Fit Trainer*
Level 2 Clone (Semi-Clone) - Mario & Luigi, Fox & Falco, Ness & Lucas, C. Falcon & Ganondorf
Not a Clone - Everyone else.
*If he is a playable character.
Some "clones" in Smash 4 would make total sense. Like what happened to Dr. Mario in P:M, Lucina as a swap for Marth, Ninten could be for Ness, etc.
I'm not looking forward to many Semi-Clones in Smash 4 though. I don't see many characters left who would make good Semi-Clones.