You can toss all of your theories of why the bike handled poorly out the window, except for the part about putting weight up front. Front panniers may not be in the budget, but can you manage a cheapo Nashbar low rider front rack? If so, get that rack and put your panniers on the front. Bam, your bike will handle much better just like that. Then take some of that gear and strap it to the top of the rear rack that you already have. That’s free assuming you have a small bag of some sort and some rope or something. Otherwise hit up Goodwill for a small bag and it’s close to free. Put a small amount of heavy, compact items on the rear rack if only running two panniers in front. The bulk of your gear/weight should be in the front. Then you won’t have any of that squirrelly “tail wagging the dog” handling. Light load? Put it in the rear. Heavy load? Put the bulk of it in the front. The bike actually handles better with the load in the front either way, but riding with no hands is easier with the light load in the rear since you can pack lazy and not worry about balancing the weight evenly on each side. If you search you’ll find many people in many threads talking about how a front biased load handles better. As for the 40 spoke rear wheel, people used to load more weight on the bike in general. You have 32lbs. That might have been 52lbs 20yrs ago. That between front and rear, and then consider that the bulk of your weight(150-250lbs?) is on the rear wheel. Wheels were also built with less spoke tention and weaker spokes back then. You won’t find 40 spoke wheels much anymore, even on hardcore touring bikes. As for evrything feeling better the next day, maybe you just got used to it? I know I still do that at the start of a tour when I haven’t ridden loaded in a while, and I’ve done a couple decently long tours now.