I can see the spells part, but smiting doesn't factor anything about CHA into it, so higher STR (or DEX) would improve the chances of landing a hit and thus allowing you to smite more often as you choose to.
Which is another tweak I would like to see--removing smites and just having smites as spells. THEN perhaps CHA would be more of a factor.
I think another factor is how far you get to play the character. Is CHA 20 obtainable by the time you stop playing the PC? Paladins are such MAD characters, that I just don't see it often. IIRC CHA 16 is the highest I've seen a paladin get in play.