Supply and demand curves don't address the customer's awareness and perceptions at all price increases. Sure if the price doubles, they'll notice. But a 5-10% increase in something infrequently purchased would not be noticeable to the average consumer. Now if it's something they purchase everyday? They'd notice a penny increase.
Yes. This is exactly the question answered by the concept of supply and demand curves. Of course you can argue about the shape of those curves but their existence is not in doubt.