If you aren't spending Bitcoin your not really helping it grow but relying on others if theres no one buying anything with bitcoin is becomes obsolete and more of a colllatable than anything else.
Wouldn't hoarding bitcoin be better? The more people hoard the bitcoin the less there is in the general public, thus making each Bitcoin value increase in value. When Bitcoin increases in value people are more interested in it and will start purchasing more.
IMO, in the short term, spending bitcoin is like selling bitcoin on exchange, and may cause bitcoin price to go down.
But in the long term, spending bitcoin makes the bitcoin system more healthy as a currency, and attracts more people to accept and use bitcoin.