If the value of Bitcoin Cash is expected to go up, why would anyone ever spend it?

An individual that holds their cryptocurrency and spends only their fiat money will eventually run out of fiat money, and thus either spend their cryptocurrency or starve (or become homeless, everyone needs to pay for rent and food). In practice, people have all kinds of things they want today (and not tomorrow) even if delaying their gratification would potentially produce a small profit. The entire point of money is to spend it on something else (or bequeath it in inheritance, for someone else to spend) and cryptocurrency is just money. Consider that a newer, cooler, faster, cheaper mobile phone is always available 6 months in the future compared to today, and yet mobile phone sales are perpetually strong since people want what's available now.

An individual that understands Bitcoin Cash is expected to rise against endlessly printed fiat currencies, will also tend to allocate a larger and larger share of their net worth into it (subject to their individual financial circumstances and ability to handle price fluctuations), until they have little or no fiat currency remaining. This reallocation leads to spending crypto by necessity as well.

As the price of Bitcoin Cash (or other cryptocurrencies) rise against fiat currencies (such as the US Dollar), holders of cryptocurrency tend to spend more often rather than less, a phenomenon known as "The Wealth Effect". For example, if a user has $10 of BCH, which rises to be worth $20, they may decide to make a $5 purchase of something they already had their eye on since it feels to them like they have received $10 of "free" money through price appreciation and can justify treating themselves.

This kind of price appreciation will become expected throughout the economy, as economic growth benefits all BCH holders due to the limited supply (resulting in lower prices) instead of the fiat system where economic growth benefiting consumers is largely offset by the simultaneous fresh currency inflation printed by the government devaluing their existing fiat savings.