My guess is that I've been watering way too much.

That is a good guess and the most likely since both mealyness and bland taste are watering related issues. Reducing the watering to the point where it is needed by the plants will help both.

Dave

Dave tells the truth on this matter. Taking it a step further, if you happen to have one particular plant with enough fruit set already there, you do have the option of ceasing all water, bringing the plant into attention mode. As well as eating hopefully a better tasting tomato sooner.

This is your plant and your choice. I have done this before, and if you have a problem killing a plant from lack of water, I wouldn't recommend it. But I do not.

If I come to a point of being satisfied with a cerain amount of fruit, I usually am happy with cutting all water, letting the plant die, and harvesting quickly ripened, good-tasting tomatoes. However, since you mentioned two viners.

Take care,
Travis