In brief: "Not very."
It's much more important to demonstrate a rough, working product that has customers willing to use it rather than a shiny prototype that has no customers.
By the time you're seeking VCs or angel funders you should be able to speak in terms of how many people are using the product and what your real expectations of a customer base are based on real-world feedback.
The question you need to be asking potential customers is less "would you use this?" and more "how would you use this?", "what would make this perfect for you?", and "how would this change the way you do things now?".
To this end, get a minimum viable product in front of customers and run through the build-measure-learn feedback loop. Accelerate the application of your learnings into the product, get some passionate early adopters and build a community of support that you can then take to investors as validation of the ideas.
Of course, you could also learn from this exercise that your product isn't that interesting to customers. Better to learn that cheaply rather than after sinking a lot of money, blood, sweat & tears into a polished/pretty prototype.