I devote lots of time to what I already have.
even with no layout and just a test track, stuff still gets broken/fixed/rebuilt/salvaged.
As a father of teenaged children, allow me to offer you a little advice.
I have provided my son with O-gauge items every year for Christmas, and sometimes birthdays. He's proud of his collection, just not as interested in it due to computers, GUITAR HERO, football cards, etc. He still likes to do the carpentry work on the layout, but rarely runs trains anymore...so the purchases have curtailed a bit (for now).
What I'm trying to say is if you have a layout in your home, and it's collecting dust, your folks aren't going to feel compelled to contribute their monies to your effort. If, on the other hand, they see you spending time on it, they will naturally want to nurture your creativity.
...and when they want to know what you want for your birthday...