Those are all very good thoughts. I find myself concentrating on #4 -- a lot.
It's important to enjoy both the building process and the finished product. Expanding one's skill envelope more deliberately helps keep the problem solving frustrations at a manageable level. One also has to accept that things are not always going to proceed as we would like. I seem to specialize in painting disasters.
I'm discovering that my personal key to having a pleasing model is a good body. For me, that means good prep, priming, and paint. I'm not quite there yet, but I'm closing in on a set of practices that work for me. I'm hoping that gets to be routine by the end of 2011.
I can't recall a better time to be building model cars. We have better glues, paints, and fillers than we did as kids. Plus, I'm much better at not cutting myself these days. We also have much better access to tools.
Our primary goal is to have fun building it, and have something we enjoy looking at afterward.
With regard to your last point about subjects, I've decided to do something I've never done. I'm mostly building to the theme nights for our model car club. My first foray into that little world was fun. I'm still building things I like, but now I get to share the results with friends.
Which leads to my last point; see if there's a nice model car club in your area. All clubs seem a bit cliquish at first, but the one here in San Diego is as nice a group of people as you could ever hope to meet.