A good measure of the utility of a payment system is the amount of fees people are willing to pay to use it. Currently, people are paying $250,000 per day. I wonder how that compares to other payment systems.
May not be strictly true. If the block size increases, the utility of the Bitcoin system will increase. But I suspect the overall transaction fees people pay to miners will come down.
The fee will go down if the block size is increased. But that will attract more users.