Well, the temp doesn't drop quite as much when you add ingredients to a hot skillet with cast iron due to extra mass-- but aluminum has a higher specific heat so it's close. Q= mc delta T
As far as reacting to acidity, if you had exposed iron it could affect flavor. But if the cast iron is well seasoned, your tomatoes are only touching carbon and shouldn't react. I cooked tomatoes in a cast iron skillet tonight.