ftfy.

It doesn't matter what unit of denomination you keep your books in. The real judge of value is "what can I buy with it" -

at the time you bought your avalon with btc... you could have instead bought 1000 USD or 242 gallon of petrol. This is a valuation of what you spent to purchase the goods. It is incidental that what you chose to buy has the function of generating bitcoins for you. This is called income.

The key is use the same method of valuation for your income as you have for your expenditure.

So what if bitcoins increase in value and have a higher price on your exchange... as long as you can spend some of those bitcoins and buy you 1000 usd or 242 gallons of petrol... as long as you do spend the income.... you've made 100% ROI on your investment.

You're confusing speculation and capital gains with income and expenditure.