The question of whether dressing should be dry or gummy is strictly a matter of personal preference, so the best recommendation is to follow the recipe exactly, especially in terms of the amount of liquid that's added. However, if you follow the recipe and think it's too dry, you can always add a little more warm chicken broth and bake just a little bit longer to incorporate the broth. If the dressing is too gummy, you can bake it longer, uncovered, to dry it out a bit.