Recently had booked Inside Guarantee for 1A price and got upgraded to a balcony. This was on Carnival. We are Platinum, so maybe that was the reason.
Also, have been upgraded twice on HAL from inside to outside cabin. First time was on our first HAL cruise.
I never, ever assume we will be upgraded and I, too, am a fan of the 1A cabins. Just get me on a ship and I'm a happy camper....um, make that a happy sailor.