Escavador,
I feel your pain. My ex wife was completly blind to her side of the family. They were always asking for help and coming up with projects for me to do. It got so bad that they'd go shopping and call to see when I'd be free to do these things they'd see that they wanted at Home Depot or some other place.
He actually asked me how long it would take me to replace his gutters and put in downspouts!! He never asked if I had the time to do it or if I even would. He was worried it might rain and that it was something I had to do real quick.
Another time I got tricked into "helping" them install some low voltage lighting in their yard. We were there for Easter and he said he didn't understand how to install the low voltage lights and wondered if I could give him a hand. I was already there, so I said sure. He helped by bringing the box of lights out, than went inside. I started without him, but after an hour I realized he hadn't come back out. He was inside watching TV. So I sat down next to him until we left.
Nobody liked that, but I was pissed off. That was the last straw for me,not even my ex could defend him after that.
The one time we asked them for some help on painting the inside of the house, they were too busy. Turns out they went to the flea market shoping and then out to eat.
Dealing with a blind spot that people have for family is just about the most frustarting thing you can have happen. Everything they do is just so generous of them, and everything you do is never enough. Pointing this out just makes you out to be the bad guy and she will defend them even more. It's a lose-lose situation.
Since your wife is making part of the tractor payment, have you considered having her do the work??? Lots of people like to plan jobs for you, but none want to actually do it themselves. Listen to her reasons why she can't do it, and use them yourself. Don't fall into the trap that your better at it, or that you know how and she doesn't, because you had to learn someplace too. If she wants it done, than there's no reason she can't learn how to do it herself.
Good luck,
Eddie