How to get a thicker soup from watery tomatoes?
One thing you can do is dry off much of the water by slow-roasting the tomatoes in the oven first, similar to what I do in this risotto. I think you will get a more complex flavor than if you boil the heck out of them in a pot to reduce. I was also going to suggest pureeing them and then hanging them in a cheesecloth bag to drain the water, but you'll lose too much flavor that way.