My emotions are my moral guides in making decisions. So i look at it that emotions add color to my decisions. The danger is always anger though.

Yes, that's what they're for. No, reason and logic take a back seat when you're upset and angry.

I have never seen an emotional world champion poker player. I have never seen an angry grand champion chess player. I could list many more thought intensive occupations that require a calm demeanor which stand as empirical evidence to the link between mental state and thought precision.

Statistically, certain emotions can encourage snap decisions. This was in my Statistics textbook, and it was also in The Brain Diet by Dr. Alan C. Logan, because they are necessarily a detraction from the use of the higher functioning regions of the brain. Emotions are necessarily just chemical reactions and don't have a real cognitive component, but they boost physicality which can increase something called "penetration of mind", which is an excellent term from Dr. Joseph Simms.

It seems like the only emotions that are good for thinking are interest, being in "the zone", and such.

Hard to say. Emotions definitely play a role in everything we do. Some more than others.

I think if we let our emotions lead us around by the nose, yes. If we change our relationship to our emotions and stop identifying with them then we can allow them to pass with incident, even when they are feelings of anger or extreme distress.

I find martial training helped me focus during times of immediate crisis.
As for spats and arguments, there is a pattern I notice. The focus turns from the bone of contention to making the other person feel as wretched as you do through name calling and pointing out irrelevant flaws.