So shouldn't the only question ever be:

* Would we rather burn computing resources (i.e. on new threads) or calendar time+human resources (i.e. on code refactoring)?

Followed closely by:

* And does it even matter for our situation? (i.e. since for many situations getting every last drop of performance out of a system isn't the real obstacle; it's making it do something useful for the end-user or business)