Bribo,
Don't get discouraged and quit. The only way to get better is to keep trying something until you get it. Based on what you are describing, I think that you have two problems...
1) Your wash is too thin.
2) Your surface is too glossy. Try applying your wash to a semi-gloss or flat finish. You have to dullcoat most models anyway, and these finishes have much more "tooth" to them than a gloss one.
I do acrylic and water color washes and they work for me. They are a little "safer" because they don't attack paint except for other acrylics that are fresh.
When you use a water based wash, you need to "cut" the wash with some liquid soap so that surface tension is eliminated. Surface tension is what is causing the water marks you see. Don't use a lot of soap, or you will get bubbles, just enough to allow the wash to "flow." A good test is to pick a recessed panel line, then dab a brush with some wash in it. If the wash is cut right, then it will shoot down the panel line on its own via capillary action.
The really nice thing about using water colors (which is what I mainly use) is that if you hate the wash, it comes right off the model. Once you are done, you can seal it for protection.
You can also try a "sludge" wash which is a drier wash. Simply make a thicker solution of paint and really goop it on the panels or items being washed. Let dry completely and then clean off the excess. This technique may also help you.
Hope I have helped, and hang in there!!! Remember, hobbies are fun.
Scott