At the end of the day, in order for the price of bitcoin to increase over the long term, it needs to be used by a larger user base, and each member of the user base needs to use it for a greater share of the total commerce they take part of. Both of these will require much larger block sizes.
This is not what I would agree with.
If I have 1 BTC then why do I need a bigger block size?
In time if my 1 BTC is going to buy me a house then the tx for buying that house will actually be tiny (it certainly won't require a bigger block size).
If your goal is for your 1 BTC to be able to buy a house in the future, then the price of 1 BTC needs to increase.
The reason why the US Dollar is worth so much is because the US Dollar is used (and accepted) all around the world (it is used as part of a very high percentage of worldwide transactions). Many other government fiat currencies have similar correlation. It has often been speculated that new merchants accepting bitcoin would be positive for bitcoin's price.
Why would someone buy 1 BTC for several hundred thousand dollars (or a fraction of 1 BTC that makes 1 BTC worth several hundred thousand dollars)? The answer ultimately needs to be because they can spend parts of that 1 BTC at a wide variety of merchants and have the total cost be less then using credit cards and physical cash. In order for the price to go from ~$385 to ~$300k, a very large number of people need to buy 1 BTC, and as stated above, they will want to spend that 1 BTC.
Granted some people may buy 1 BTC in order to speculate that the price of BTC will increase, however the price increases from speculators is limited and there needs to be reasons other then speculation that the price of BTC will rise in the future to buy BTC.
Your transaction to buy your house is going to be a very small one (in terms of blockchain size), however in order for your 1 BTC to be valuable enough to buy a house, then many other people need to be buying (and spending) BTC at the same time.