Well, I guess I've gone as far as I want to go with this model - it was just a practise model after all. It's achieved everything I wanted it to, I've brushed off my Google SketchUp skills and discovered new techniques in rendering (something I've always wanted to explore).
The model itself is a bit basic, and I've fudges some of it - not wanting to get sucked into complex detail when all I wanted to do was practise (I'll save that for 'live' projects).
Most of all, though, I've enjoyed myself - I was asked by someone I showed this model to 'what's it for?', well it's not for anything other than the practise and enjoyment really. I've always said that building 3D models in SketchUp is rather like building an Airfix plastic kit when you were a kid - it's a relaxing pastime which is fun, entertaining and - as you end up sharing the model via Google Warehouse (and document the process on a blog maybe) helpful to others who are learning too.