Stephen,
I don't know how your pops is, but I would get a book with great examples of suburban style japanese gardens, and tell him you want to make part or all of the yard look like that. Get him involved, and his wallet involved also. Its his yard after all, and you are hepling to beautify it. My parents would have keeled over from a heart attack if I told them I was willing to work and make their yard look like that. I never willingly did yard work as a teen. I should think they would be all for it, if you showed them pictures of what you were after.
But, on the note of japanese maples. Small ones can be had for pretty reasonable prices, and no other maple can touch them in beauty. Plus, many of them will naturally stay small. Its the named specialty varieties that get pricey. As for water features, trust me a water basin or a deer chaser will do so much more for a small area than a gravel bed(in my humble opinion), and the moisture will help tremendously for moss.
As a vote of inspiration, I have seen japanese gardens in a 10'x6' space that were so beautiful, I never wanted to leave.
