1. I wouldn't bother doing the normal exchange anymore, to be perfectly honest. As much as the "pick your own" system is expensive, it ends up being cheaper in the long run. 2. That's true, though I wonder how relevant that is. Simple fact of the matter is, if you're using Card Master, chances are it's because you're aiming to start with something specific, so you'll be using that anyways.
IMHO random is well worth it until you have a good amount of cards >80% I'd say. You get relics back for double cards and can get fly expensive ones by chance. So buying is just good for the last 10- 20 cards that are missing or when you need that 1 card
The only issue I have with the default system, is that it overwhelmingly means nothing. The gameplay difference between a gold card and a standard means nothing in all but one level, or with all but one hero. So they don't matter for allowing new strategies. And in my experience, I was getting inundated with gold copies I didn't need versus the Legendary or Epic cards I wanted.
you can still see the starting tower prompts, you're just to slow picking your card from card master, if you pick it fast enough then you still see the prompts :)