Sadly, I fear, like Bogdan implied in a comment, that the answer is largely going to be 'no'.
That being said, there are some things you can do. One of the biggest would be measurement. After you finish a project, start inspecting and recording its actual financial impact. Measuring the past is always going to be much more precise than estimating the future, so you should be able to get relatively reliable data from this.
Then, when it comes time to estimate Project D, you can look at your data, compare it to similar previous projects A and C, and use their impact as a guideline to inform your new estimate. Stil ultimately gut-feeling-based, but at least it has some actual data involved.
Further, also as Bogdan suggested, consider an agile approach. If you're only working in 2-week increments as opposed to multiple-month projects, then you have two advantages:
- The work is smaller and thus easier to estimate
- If you got the estimate wrong, then worst-case you've only lost 2 weeks on low-priority work.