You have some good questions... I'm not sure I'll be able to answer them very well, though. I'll try.
Intention is perhaps the beginning of the process of achieving a specific outcome. For me it is usually visualizing what I want, followed by a congruent feeling that this is what I want to achieve. It may also be a feeling of openess, if I'm not certain of the specifics of the outcome. I'll set the general intention of what I want, and let the universe fill in the rest, so to speak. Some people are more auditory, and will say what they want in their mind.
I think that being more conscious of how you set your intentions, will help to filter out anything that isn't in your best interest. Writing it down helps, if you want your outcome to be more clear and detailed.
If you've made a tape, then you've already set the conscious intention that you're unconscious will follow the instructions on the tape while you sleep. However, from what i understand the unconscious mind has a wisdom of its own, and will filter out any instructions that isn't in accordance with your beliefs.
If you don't like to be told what to do, perhaps you could make the instructions more open-ended.. like "Ok, John.. now that you're asleep, what are the best experiences you could think of having? Any specific place you want to go?"
I haven't tried that myself, but it's worth a try.
Also, I think Bruce wrote an article about using intention.. something about learning to recognize intention by bending a finger. Or maybe it was in one of his books?