As others have said, think of your Apple Watch app as an extension to your iOS app's UI: it enhances your iOS app vs. the competition that doesn't offer the wrist UI.

I've seen users requesting a Watch version in reviews for iOS apps. Even I have chosen some apps in the past over others specifically because they offered a Watch app, like navigation apps and flight checkers etc.

As a user though, I must say that if "monetizing" and "selling on its own" are more important concerns for you than make your product/service a better experience for ME, then I probably wouldn't want to use any of your apps.