You should spend bitcoin to help the bitcoin economy.
If you made a lot of profit you owe taxes on any bitcoin you spend. Capital gains or w.e applies in your country.

MUCH smarter idea is simply buy new bitcoin today, and use that to spend. That way you help the bitcoin economy, you don't incur tax implications and you create buy pressure prior to the sell pressure any merchant you buy something using BTC will create when they sell that BTC you just gave them. Most merchants will sell it for fiat or use a service that does this directly without them even handling any bitcoin ever. They only want revenue from increased sales, they are not in it to hodl (Overstock is an exception).

P/s: Don't spend your investment bitcoin unless you want to pay taxes on the profit. Capital gains apply. You can buy fresh new bitcoin today right now to spend on purchases if you want to spend bitcoin to help the bitcoin economy.