It feels like Scorcese is throwing in and wasting a lot of talent - Wahlberg and Sheen are totally not needed.
I think of them as spices to the greater dish. If The Departed didn't have them, I wouldn't have liked it as much. Too bland of a taste.
Your food analogy is a great one, but you're COMPLETELY WRONG!. Like all good flavour combinations (apart from perhaps in Asian cooking - Infernal Affairs? Er, maybe the metaphor doesn't... anyway), it works best when you just have a few srtrong flavours, or you end up with something that has no real flavour to it at all - like the way you mix a vivid red, blue and yellow, but end up with a murky brown.
I'm one of the few who liked Jack's chilli pepper, but I have to admit that Leo's.... star anise? - won the day.
To be honest, they could have replaced Wahlberg with Sean Hayes from Will and Grace and nobody would have noticed the difference. Not a good addition to the pot.
(And Phil, I mean the actors were bad choices, not that the characters were not needed. )