Just be realistic about your expectations.
Are you prepared to pay more in your monthly boarding fee to have this things done? All of them cost, both in time and money. Do your BOs have the equipment, time and experience to make these repairs themselves, or would they have to hire them out?
Put yourself in their shoes - if you accepted the conditions when you moved your horse there, is there a compelling reason for them to change the conditions?
I like tim's suggestion, you'll get much farther by saying "I'd really like the round pen set up differently, if I did the labor and/or bought the materials, would you be willing to....?" or "I'd really love the pasture mown, I understand it's expensive, would you consider mowing more often if I paid for the diesel fuel for the tractor?"