I plan on flushing my cooling system soon and I'm planning on putting wet-wetter additive in there because import tuner proved that it worked. But does anyone have any opinions on cooling additives in general (royal purple, wet-wetter, etc.) or a link to a reputable place that has reviewed these kind of additives.

 

Water wetter is very good. Since you live in Sac and it doesn't get that cold you can run very little anti-freeze type coolant. I would run like 10% just in case you have a cold snap. Water has about twice the heat removing capacity that anti-freeze so combined with the water wetter it will remove heat very effectively. The only time you should run more is if you occasionally go up to Tahoe or something where it gets below freezing.