I wouldn't recommend cooking tomatoes in cast iron. It really isn't a great combo, and also can mess with the flavor of your dish. Also, don't cook them in aluminum.

I wash my cast iron with hot water and soap regularly; after every time I use it. However, I do it quickly. It doesn't take the seasoning off, but my pan is probably seasoned quite well. It's incredibly non-stick. Fresh potatoes for home fries do not stick. That's generally a pretty good test. Techniques also play a part, but my cast iron is almost as non-stick as my actual non-stick pans.