I built a SaaS product, but it's too early to say if it's a valid idea yet. What I did do was find 5 companies with the same problem, and gave them free, very early access with regular calls for feedback. Interestingly, several were very precise in their requirements, and others were open to my approach and ideas. It's important not to try and implement every suggestion you're given if it doesn't feel 'right', otherwise you risk creating a product that's inflexible for everyone except the customer who asked for it. Try and find a sample of people who will give you the time of day.