That is a very 2015 view - now days people don't buy bitcoin for its use in transactions, they buy bitcoin because it keeps going up. The more it goes up the less people are likely to spend it. We don't need many miners if people never spend it. Here is one high profile example http://avc.com/2017/08/store-of-value-vs-payment-system/ (of course when it starts to go back to zero people will all try to sell and the inf…
Data shows otherwise. Bitcoin speculators typically leave the coins in an exchange wallet (not sufficiently technically savvy or motivated to run their own wallet). Doing so does not create a transaction on the blockchain, therefore the transaction rate (https://blockchain.info/charts/n-transactions?timespan=all&d...) reflects mostly non-investment-related transactions, and it is sharply increasing.
«The more it goes up the less people are likely to spend it.»
Historically, transaction processors like BitPay have noticed precisely the opposite. I guess people are excited to spend their newfound fortune when BTC goes up? I observe this behavior on myself: I cash out and spend more bitcoins whenever the value is going up (Jun 2011, Nov 2013, today, etc)