What is the bonus of keeping a highsec pos running after I have finished researching all of my BPOs? As the only ones I have left to purchase are the Capitol BPOs.
Highsec POSes have a few other "bonuses" even when you're done researching every BPO you have (and even then, really? you can't find anything else to research? :P )
The big one is for manufacturing modules and components. The manufacturing arrays for said do not consume any more resources than a station's assembly lines, and they have considerable time bonuses, meaning your manufacturing jobs are going to get completed sooner, and you can produce more. Additionally, using the arrays does not cost you ISK (though maintaining your POS does).