I do not see any issue at all with adding water. I personally like adding real coconut milk in my smoothies for more body and creaminess. I have a Ninja bullet style blender that does what a juicer does but leaves all the fiber in the smoothie.
My recipes are usually what is in the fridge. For breakfast I will freeze a half a banana and the other fruits the night before. To my fruit smoothies I will add a tsp of a vegetable based protein powder for extra amino acids, ½ tsp of Chia seeds, ¼ tsp cinnamon, and I a tsp of psyllium powder for an additional fiber boost. I will add water if it is coming out on the thick side. You can also balance out the sweetness by mixing in less ripe fruits with the riper sweeter fruits. I don’t think kale is all that offensive and will add that in the my fruit smoothies but if makes it look yucky but won’t kill the flavor of the fruits.
For veggie juice/smoothies again it is anything goes. I haven’t yet found a way to offset the bitterness of raw spinach and broccoli but am still experimenting. It may just be adding less of the more bitter raw veggies. Sweet red pepper is great for adding flavor but just a smallis slice is more than enough to add a nice flavor to the mix.
For veggie mixes I don’t freeze the veggies and will use crushed ice. if I have it I like to add a couple tablespoons of that coconut milk, a chunk of pineapple and or a slice of pear to sweeten things up. Again a tsp of veg based protein powder and tsp Chia seeds. I also like to flavor things up with some fresh herbs and lemon. Fresh Rosemary, a squeeze of lemon juice or fresh lemon mint leaves are my fav.