Correct, which is why people need to make up their minds whether they're investing in a currency or a store of value.

In a large economy, the only way to keep prices stable as the size of the economy expands is to expand the money supply as well. This can be done in 2 ways:

1. a central bank can issue more currency
2. the market can issue more "currency" by way of derivatives such as credit capital etc (i.e. denominated in the monetary base but backed by new debt instead of blockchain tokens - see example below)

So by virtue of point 2, a fixed supply monetary base could still work as a currency denomination, but then your not using the blockchain as a "payment system".

This is something that has to be broken apart and thought about a whole lot more than it has I think - not just in Dash but right across cryptocurrency. You are right that the main function of cryptos will probably be "hoarding" (otherwise known as investing in a monetary asset for the purposes of preserving/gaining value) because the limited supply kind of guarantees its value against non-limited supply currencies as long as adoption is reasonably stable.

Of course, it's important for money to be mobile, since liquidity is a big factor in its performance as a store of value. So "spending" in that sense is applicable and must be easy to access/use. But I see that as being distinct from a "payment system" which is generally currency agnostic and simply facilitates trades such as POS, eCommerce etc.

Lots of different aspects to decouple from each other and well beyond the scope of one post.

*************************************** P.S. *****************************************
Not a lot of people realise that 2 already happens right now. Exchanges extend the effective money supply by "adding" credit money to the monetary base on the blockchain. That credit money is backed by the exchange's contract with you when you make a deposit, denominated in the blockchain denomination concerned and all subsequent trades are then carried out off-chain at instant speeds.

In my opinion, if cryptos ever see major retail adoption, this will be the model they'll use. Blockchains will not be used as payment systems because a payment system needs to be currency agnostic, massively scaleable, instant, reversible...i.e. all the things that blockchains "aren't"