I was thinking about this idea along with other ideas to start a side project. I want people have one stop for all financial things. Allow people to track their networth on a time to time basis. It also allows them to budget efficiently. Keep all the finance related documents (car loans, Motgage, student loan ) in one place . define long term financial goals and track them accordingly. How many would like to use a service like this ?
I would definitely use a such tool...
Years ago, when I was starting as developer, I've also write my own version; it just tracked expenses and incomes.
One question a such tool should help answer is where did my money goes... but this is particularly hard for cash payments.
For example, the app I had written was not good at this, and this was the main cause for me stopping to use, work on it.