I have done some prototyping and got an MVP of a service (web/email marketing, very niche), that was sort of a pet-project you write just because it makes you feel good.
Now I see some value in the idea itself, and looks like I need to find some business co-founder, who can ramp up the business processes, customer traction etc.
I know that every single book recommends to validate an idea first, and then go with the implementation. Is it a dead-end in my case?
Find people who would benefit from your service and tell them about it. If they sign up, there's your validation.
If your service is not solving a problem for them, the road ahead is tougher, but it's still not a lost cause. Talk to prospective customers about the problems they're having and how they deal with them. Is there a pivot you can make with your service that will solve one of their problems?
The difficulty here is that, when all you have is a hammer, every problem looks like a nail. You're likely to see ways your service can help them with minor tweaks where, if you had talked to customers first, you probably would have built something different to solve the problem. Just be receptive to the idea that maybe your service doesn't have a market. You'll learn that from your customers if you keep your ears open.
Doesn't mean you can't then go and build the perfect solution for them and sell them that.
I'd like to chat with you. Email me please, it sounds like something I can help with.