I would first use it myself and see the results within a few months. If it works as you hope (or better!) then I would just keep registering / buying domains to add it to. If it's mostly automated, then scaling it shouldn't be an issue.
Basically, if you have something automated that can generate 1 sale per month per domain, or even every few months, AND it can keep that result for hundreds or thousands of domains then you should have no need to do anything else with it.
Basically, it will come down to do you want the recognition of having a product out there to help other people make easy money, as long as it doesn't hurt your own pocket? If you do and believe the hassle is worth it then, by all means go ahead. If you could care less, enjoy your free time instead
Of course, if it fails for your own tests, then it's a useless service and you shouldn't consider selling it as a service until it's been properly tweaked to be successful.