The point you're missing is the fact there needs to be two chronologically separated exchange rates for this
No, you only need one exchange rate. The one at the time of purchase. If you paid in BTC for your gear, you don't even need that.
At every point in time, having 65 BTC is better than having 60 BTC. If the exchange rate goes up and you choose to have 60 BTC, you are worse off than if you had chosen to have 65 BTC.
If you bought 10 BTC over the counter for $10,000 when MtGox was trading BTC at $100 each. then held the BTC until they were each worth $1001, then sold them, did you win? Should you be happy with that investment? Would you repeat it in the future?