Instead of trying to add up the costs/income per property, why not do it per week?
It's easy to say "well, I have this property up and cash flowing, so the return on my time this week is infinite for this one". But in reality, aren't you spending time looking for new deals, managing other properties, etc?
If you just look at total income (from all your properties) and total hours per week spent (for all current and future properties) on real estate activities, that should give you a quicker "snapshot" of your _current_ (not potential future, which ought to be the area where you are killing it) income per hour.
I have a friend who is a professional in a well compensated field, in mid to late career (mid-40s). If he makes $200 per hour for his 40 hours of work each week (which he does, roughly, and yes, it's really 40 hours), is real estate investing a worthwhile activity for him? Can he expect it to increase his average hourly income within the foreseeable (5-10 years) future? Or will it drop his average hourly income for longer?
Remember that in this stage of life, his primary goal is to spend more time with his family--not to build additional net worth (that's already doing fine).