<font color="red"> The original post was about an all around tractor, not lawn machine, and I find the lighter ones just don't fit the bill. </font>
MMM, I think your own words here are betraying you. The original poster is looking for something that does a bit of everythihng. A heavy machine probably has some inherant advantage with a FEL and when using plows, disks, etc on the 3pt that engage the ground. I doubt a lot of people would argue that. I think many will argue that excess weight on a small CUT tractor is not an advantage. Further, we are talking about CUTs in this thread, and fairly small ones at that. It sure seems like you are talking about larger machines intended for different purposes, and you certainly admit that you are not using it for mowing the lawn. Well the original poster needs to do that. As do many others who own small CUTs; most of the people who post on this site seem to mow some sort of lawn with their CUT.
As someone who has used many loaders in the past (desk jockey now) I can tell you that no CUT or even UT will do the work a loader will do. They are different animals. And yes, weight on a loader is important, on the back end as counter-weight, or if you prefer the term Neil used, as ballast. The thought that a heavier tractor has more built in ballast is not really true. Most tractors, contrary to popular belief, are front heavy, they are designed that way becuase the implements hang off the rear, and they need ballast in the front to hold front end down so the front tires get traction. The rear tires get plenty of weight from the implement itself. Loaders change that equasion of front to rear weight distribution and throw more weight on the front. A heavier tractor may be able to lift a bit more than a lighter tractor without any ballast, but that is not to say that it is generally a safe thing to do. That is why rear tires get loaded, to make it safe if you are doing a lot of loader work. It balances the weight distribution so the tractor doesn't tip onto its nose.
If we go back to the original post, DAP is refering to a fairly small (30hp) CUT for all around use. He stated the particular model is too much tractor. We all spun off into the weight debate. Now if we want to move the debate to the type of tractors that you use on your farm, then I would say that no CUT is going to do what you want, not a light one, and not a heavy one. CUTs are really not made for picking up round bales of hay or other big jobs. (yes I admit some of the big CUTs can work a bale spear, but the utility tractors are really designed for those types of chores while CUTs are generally not, especially in the under 40hp classes and certainly none in the 30hp range like we are talking about in this particular thread).
Generally I think Neil Messick's post is one of the most informative and accurate posts I've ever seen on TBN regarding weight for MOST of the CUT users who have 1 CUT and use it as an all around machine that does loader work, mows the lawn, powers a few PTO implements and pulls a few non-powered implements like a rake. As we get into specific users and their specific uses, then we get into hot water (we all know I've stuck my foot in that a few times). I have some slopes, so I have some specific issues I deal with, and I typically state a disclaimer of some sort if my slopes were part of my equasion for my decision. I also have clay soil that easily ruts when wet and my hobby of playing with antique tractors has the lovely Mrs_Bob pointing to R1 tire tracks in her lawn when I take an old tractor out even a week after the rain stopped. So my personal experiences bias my needs, but I think I try to discuss many points by putting disclaimers or by talking about what the average or typical user might consider necessary. I think for most CUT users, there is no inherant advantage to heavier than necessary machines.