I think if you don't play any cards you can scrap 1 card would be more appropriate. Buying cards once you have some good cards is the least important part of your turn and being able to scrap whenever infringes on the red faction.
Agreed. It would be very easy to get an early power card or two, and then simply stop buying until you thin your deck down to a few big cards. That's the weakness of not splashing red into your deck; your ally effects won't trigger as often.
It would also gives rush decks a big bonus, since one big weakness is the fact that they have to deal with their starting cards for so long. Imagine if a blob deck could phase out its scouts simply by not buying, which wouldn't hurt them much once they're playing a fighter and ram or two every turn.