We have the 4x4 DK45 with cab and FEL as well as a small Ford 1300 for smaller jobs but we have about 20 acres we plant an maintain distributed across the farm. For some tasks I wish the DK45 was a DK65 instead. For other, the little Ford is perfect and much more efficient. I also have an older Kawasaki Prairie that I got primarily for hunting and deer retrieval. It has a Great Day's deer loader on the front and I rigged a large utility box and basket on the rear for transporting stuff. I end up using it for a lot of work though. I use it to transport ladders and stuff for deer stand and camera maintenance, planting trees, grafting, maintaining trees, and all kinds of similar tasks.
The last time I took the Prairie in for maintenance, they wanted more to get it up to snuff than it is worth. I think I am simply over loading it and asking it to do more than it was designed to do. I decided to have the minimum work done to keep it operating and started to look into replacing it with a Honda UTV. I have not pulled the trigger on that yet and it may be a while before I do.
This just goes to emphasize your point that pushing any piece of equipment beyond what it was designed to do will increase maintenance cost and reduce the lifespan. I'm not even dragging a disk or doing planting tasks with it. I did do some spraying with it but I could see how much stress 25 gal of water was putting on the suspension. I ended up buying a carryall from TSC and installing the boomless ATV sprayer on it. The ford does an even better job than the ATV for boomless tasks since it holds a constant speed and the weight is nothing for the ford.
Thanks,
Jack