-"You've built a web app, but your users stick to Excel"
I feel that if your users are not using your web app, it's not because they miss the (dated, not exactly intuitive) Excel interface. Seems to me like the wrong solution for the problem
I just don't understand how companies can think this kind of privacy invading marketing can be effective. In which situation do they believe they are adding affinity for their product by scraping your email?
I would say never actually look for problems. Certainly, never start with the solution and work back to find the problem. Train yourself to stop and think when you encounter a difficulty. Learn to ask yourself if there can be a better (faster, cheaper, automated) way. If you have an answer, THAT is your idea
What are you suggesting? Is the idea to allow potential users to put some money down, or to show interest before a startup idea is fully executed? If so, you can do that pretty well with a landing page and a sign up form.