Hey Steve,
You make several good points, but there a few that are iffy.
You're right that 4wd won't overcome a 30 hp spread from 20 to 50 hp, BUT it will absolutely overcome a spread of 15 hp. Had oldtimer said his 20 horse will beat a 35 hp 2wd, he'd be right. You're also wrong about 4wd being less important on bigger tractors. Most new machines these days have 4wd. You would have a hard time finding a tractor manufactured in the past 15 years w/o 4wd. It isn't because a fellow is willing to pay 15K more for an ineffective option. Price out a new tractor today and the 4wd is a "Delete", not an "add" option.
I also disagree with your assessment of skid steers. Perhaps you owned a gas-powered OMC from the late 70's. I can do just about anything with a skid steer that you can do with a loader tractor and do it better. In fact, I can do more with a skid steer than you can do with a loader.
Yes, you can buy parts for a Farmall M ... at a CASE NEW HOLLAND DEALER! Would you take that M into the dealer for service? Ms are at least 57 years old and so simple that you fix just about anything on them with a locking pliers, and adjustable wrench, and baling wire. My point wasn't leveled only at IH (got one with a TA that is out or going out?
), but towards any model tractor that no longer has support. Deere is abandoning some of the less popular and older models as well. Their support of the Yanmar Deere's is slipping. I couldn't get loader brackets to mount an 80 loader to a 1050. (anyone looking for an 80 loader to mount to an 870, 970, 1070?)
I grew up on Deere and am indeed colorblind to them. We have a 1050, 2040, 3010, 3020, 4010, 2 - 4020s, 2-4430s, 4640, and 4840. We also have a 1086 sitting in the back of the shed with a blown engine and a bad TA and a Farmall M that sat in the shed for 20 years with a locked engine. Just got that one running again last year.
Maybe my point would better be rephrased as "Be careful about ANY model tractor you buy. Find out if they're supported by a local, knowledgeable dealer".