[Crimson]

It is obvious at this point that not only do people disagree greatly on this, that while interesting, the replies are becoming stagnant, so lets try and organize our thoughts. We're obviously not folding, so lets look at raising as our option, and weigh the pros and cons of that accordingly. (I picked raise because I had originally intended to do this for both raising and calling, but realized 1 would be sufficient for if its pros outweighed its cons, it would be thus).

Raising

Pros:
The obvious equity edge vs. the field.
Maybe getting a free card, depending on how aggressive our opponents are.
If the SB 3 bets, and the other opponents call, we can still cap for value. Secondly, by building the pot, when we hit, we may induce a call from someone drawing dead due to the sheer size of the pot(see Westley878's quote for these last 2 arguments.)

Cons:

It seems first and formost, we fear being 3 bet by the SB, driving out the callers, and ruining our odds.
Also, we are afraid that if we raise, and it is simply called back to us, it will be checked around if we hit. Calling allows us the opportunity to raise the turn for a bigger bet when we hit, if we fear being checked to.

Newhizzle had a few interesting statements as well, which i'll quote. "i dont necessarily agree that raising hurts our implied odds because i think people will slow down in a 4 way pot when a flush card hits anyway, and if SB just has overs, he probably wont bet the turn anyway, not knowing who will bet, you might get put into a situation where you are forced to face the field with 2 cold or go for overcalls

people are likely calling with all kinds of crap on this flop and may not plan to continue on the turn UI, plus if we up the size of the pot maybe people will keep drawing to their gutshot even if a flush card hits"

If I missed anything, I apologize, I think I hit the major points. Obviously this is paraphrased from the thread, and not new information, so it is just a recap.

Other things to consider: Player reads. How likely is the 3 bet to happen, and how likely is he to lead a spade turn if we just call with UI overs or an overpair (set at best). How likely are the callers in MP likely to call if the SB does 3 bet?

This, dispite many posters claims, is close, and in my opinion which button to hit would depend on some metagame considerations like player reads and what not.

Hope this helped. Edit to say: I'd raise.