I've done my share of Frax flying prior to working for a 91 flight department, know both pretty well. Flying Part 91 now I obviously like to look at the pros of ownership because I also don't want my job to go away. Here are some that haven't been mentioned.
If you fly a new airplane, I think asset depreciation and last year's (continuing through this year) bonus depreciation needs a little more attention on this thread than it has gotten so far. For people that HATE to pay their high (soon to be higher) taxes, any way to offset that is worth looking into. That fact alone keeps us looking at new airplanes rather than used when our depreciation schedule and warranty run out.
We operate into some smaller airports. We do not have to comply with 60% or even 80% runway rules. We use our heads and decide if it's smart to take our airplane into the 4000' strip that day or somewhere else.
If you base your aircraft at a smaller airport you may be able to leave on the days that there has been bad winter weather. We have a hangar at a small airport so if it snowed overnight we pull the airplane out and blast. Any RON's are stuck because there is no available hangar space for anything bigger than a twin Cessna. De-ice equipment is subpar to say the least.
AOG, the frax do have the edge here with being able to recover a trip. . .unless that pilot group is in a labor dispute. Look at the DA on NetJets and Flops while pilots have been in heated negotiations. Do you REALLY think the airplanes broke more during this period? No, pilots were just less motivated to carry the MEL paperwork to the next destination after the pax deplaned or refused to do one more landing when the brake wear pins were getting "close". I would never advocate flying an unsafe airplane, but I would also not inconvenience my boss with an MEL paperwork delay for a burned out nav light discovered on preflight.
If you're really looking to offset cost of ownership or hourly cost look into finding another partner. Let them buy a "share" of your jet.
Lastly, and this advice goes to all in Part 91 ops, don't let your ego buy you out of a job. When your boss asks you for research on airplane purchases, be fair to him and to yourself. Look at what you NEED, what would be NICE, and what you WANT. There are many flight departments that ended up with the X and a bank note when the paid off Ultra would do.
All that said, a smart owner will face facts. There are costs that stay the same each year (hangar, insurance, pilot salries, etc) and those costs have to be defrayed over the hourly cost of operation. There gets to a low yearly hour number where those fixed costs make the cost of ownership higher than the frax. I hope for your sake your airplane keeps flying.
That's as objective as I can be.