A potential bitcoin miner has to decide whether it's worth buying the equipment in the first place, and then later they have to decide whether it's worth it to

A potential bitcoin miner has to decide whether it's worth buying the equipment in the first place, and then later they have to decide whether it's worth it to upgrade. Before they actually start mining they're speculating that the future value will cover the up front equipment cost, on going electricity costs, and all of that. IMO, the interesting number isn't the cost of mining or the value of the bitcoins in dollars, but the value of goods and services being bought directly with bitcoin. If everybody treats it as an investment and never spends it, or immediately cashes out, then isn't it essentially just a big ponzi scheme?