G'Day thejackhome [Toscana]
It is a nice idea but will not very practical or very accurate.
WUProp has only been running this project for the last few years, yet most main projects have been running for many years longer, with some going back 15 years.
From this you can see that there is no accurate record of the hours anyone has spent running any one particular project. It is not a statistic that is kept by the projects themselves.
The only way any project currently has of saying how much effort you have put into any project is by the use of certificates stating how many GigaFLOPS you have contributed.
Even these are not accurate as they are based on validated returned results and do not include the many hours you may of put into jobs that then fail (WUProp does record all hours run an any WU so failed ones are recorded as well, the projects don't take notice of this).
I don't want to sound all gloomy as I like your idea but there is just not the records and data to put your idea in place.