The classic, moderate racing bike position evolved for a reason. Not only is it more efficient, it's more comfortable on long rides, even though it may not seem like it if you're just sitting on the bike in your living room. The more you get away from it, the more problems you have, because everything becomes unbalanced and you get too much weight where you don't want it. If you lower your saddle as you did, there is really, truly, a tremendous drop in pedaling power. This is not imaginary. Fine for a cruiser rider, but not someone who is serious enough to keep riding a road bike (a touring bike is a road bike, after all). This may be why you suddenly feel like you're less fit than you were.
Then there is the wider, more padded saddle idea. This is almost ALWAYS a bad idea on a road type bicycle. They compress and put pressure on all of your crotch, they chafe more... just bad news all around.
I'm not exactly a powerhouse either. I'm 55 and I have lots of medical issues, including an organ transplant and asthma. But I've always found that because of it, rather then detuning my road bike position, I need all the help I can get in terms of making the most of what I have. So for me, that's a road bike ridden in a moderate road racing position. I actually went through what you did, thinking that I was now too old and sick to ride like that. But it turned out to be the opposite. I gradually realized that much of the advice that can be found on the internet about "comfortable riding position", fat tires and all that are just crap.
What's a moderate road racing position? Well for me, it's my saddle adjusted a little higher than the heel on pedal method, but not as high as the "LeMond" method. It's my fore-and-aft position just a touch behind what KOPS gives me, and it's my handlebars about an inch below the saddle top but with the proper reach for me at that level. It might not work for everyone, but I would suggest that if you want to ride a lot, it's a good starting point. When you ride a road or touring bike and you deviate too much from this, this is when you willingly get on the never-ending tinkering merry-go-round because nothing feels right.