.1 BTC is definitely very low for the instant buy. In my experience, there was a 30 day hold period(Buy and hold on to BTC) along with registering a credit card for the instant buy. After that, you can buy up to 10 BTC instantly a week. How it works is if you buy x amount(up to 10), the amount of instant buy starts replenishing at a rate of (10BTC/7Days).
.1 BTC is not so bad for most, this is ideal amount for first buy and try the Bitcoin
This is true at current prices. With the crazy price fluctuations recently, I'm using it as an opportunity to "average in" until I get to the quantity I want.