Thanks a ton Mike for your effort! I will keep this short and sweet.
I finished the piece with the perspectives fixed: http://eeliskyttanen.deviantart.com/gallery/#/d5ohzfj
I think the problem was poor design rather than lack of fundamental knowledge. As I commented to David I was fearful about too strong one point in the centre, and because of that intentionally twisted the right side of the "canyon". I had a grid to work on with, so it didn't really leave room for easy mistakes. The one thing I did hastily though were the triangle things, but those are now fixed too!
I think one can definitely add quite many VP's. For example a medieval village with a lot of cluttered buildings would have huge amount of them. Correct me if I am wrong though. In this kind of a castle/ruins/huge structures piece that didn't quite work though, and I scaled it back.
Not to say that I don't still need to rehearse em basics as hard as always, but darn, after that stuff with "Pebbles" I will never ever make unintentional perspective mistakes again. Instead I will always check it up with a grid.
Again Mike, thanks a ton! Helped me to realize those stupid design decisions and fix 'em all.
EDIT: Mike, here's a nifty timelapse video for ya! David saw it already: http://www.youtube.com/watch?v=x8UWwg2k9uo