My take on this is simple. An ATV is a toy and will never be able to do the work that a tractor will be able to do. Trail maintenance and to do lists on properties always grow and get added to especially when the property is over 3 acers so that makes the tractor a NEED and the ATV a want. That is simple and would have me looking for a decent used tractor and putting a new ATV on hold till I had the tractor and the immediate work done. The tractor will hold its value long after the ATV is worth nothing but scrap. Besides you seem to have an ATV for fun already so what is wrong with keeping it for fun now and upgrading to a new toy latter on.
You stated time to do the job would require taking time from work? Vacation time should be spent with the loved ones having fun not doing work around the homestead . I would add to the cost of the rental the amount of a weeks vacation pay, then again that same pay to fully justify the time wasted on work to be done rather than enjoyment time while on vacation with the loved ones! At least tripling the actual money lost with the rental way of doing things!
My fun time with the loved ones is valuable to me and getting to the point of being able to enjoy that time, is best served with a good machine that can get the job done quickly. Today for instance I cut up then dug out a few trees cleaned up and leveled off the area then went out to the far end and moved a good bit of shale, about twice what you call a dent in your pile . The best part is I was able to do it when I felt like, never felt rushed and still had the time to pull the Bike out of the garage, wash it and take my other half for the first ride of the year. We went and met up with some friends for a nice relaxing ride and then stopped off for a good meal at one of our favorite spots.
OOPs I almost forgot about moving those two boulders out of the neighbors property for him. Poor guy was out back digging away by hand trying to expose enough of them to get them out while his little ones were out having fun with their toys (dirt bike and ATV) while his toy sat in his garage unused, what a way to spend quality time? If he had purchased a small tractor like say my old JD755 when he got his ATV a few years back instead he could have gotten a used or even a new ATV a year or two latter and actually had the pleasure of rideing with his kids rather than spending yet an other day working while they played with that WANT sitting Idle in the garage!
Shall we go into the importance of choosing a want over a need and the example you could be setting for your little one as well.