We can't include the value of the SP we already own as we get that value anyways.

I left out curation rewards on purpose as its an unknown factor. The curation rewards might be the deciding factor on if its worth it to rent SP or not. With my low voting weight I don't get much curation reward currently so I don't expect much of an increase with only being at 100 SP with a 50 SP lease.

With each vote the value of the next diminishes. So catching the eye of a few more followers will hurt your short term gain on recovering that Steem spent on renting SP.

The more upvotes you give out to others .. the more you will need to give yourself to regain your investment.

My first example was bare bones as like you said there are allot of factors to consider.

As I said.. if I do decide to test renting SP then it will likely be enough for me to get that slider. I have been testing lots and using lots of different strategies since I have arrived.

And we have to take into consideration catching the eye of those who frown upon such activities as self-upvoting.

For now I will continue with the current strategy I started last week ( while keeping a close eye on that steem price ) and see how it turns out over the next week or so before deciding to move onto another one.