I think most trainers would give you pretty much the same information. I was a semi-pro soccer player for a while in Europe, and they always suggest that you increase intensity and intervals. So if you are doing a few miles a day, the way to increase your fitness is to do more miles, and faster. It's hard to hike more than about 3.5 miles an hour without breaking into a jog...so start running. Don't worry so much about the lifting...your body has plenty of strength, and heavy upper body weight will not make you more efficient on the trails. Go for as much cardi as you can, and focus on your recovery time.

Just to give you an idea, I ride a bike about 6000 miles a year, and I go fast. And I don't have much trouble on hikes these days. I am also 5-10, but weigh 175. I'm also 57!

I'd add in some cross training ( like cycling) go farther and faster, and add some higher rate exercise and your fitness wil improve.