I'm 42, started touring 4 years ago, and I can see what you are talking about coming.
I see a LOT Of older 60-70 y/o people touring. That's when most people get enough time in their lives to do it. I met this one guy in Leadville, CO who was on his way back to Florida from Alaska. He was 82.
Geezer, in terms of the backpack/wagon analogy, it doesn't really work that way, in neither case is the weight on your body, it's on a wheel. So weight is weight, but packing and handling come into play, too.
1) handling - some people (me) experience very bad downhill handling issues with a trailer "tail wagging the dog". I actually crashed because of this. If you have any way of borrowing a trailer and trying it fully loaded on some downhills before you commit, that would be a great idea. You can buy trailers from REI, who have an amazing 100% satisfaction guarantee policy, even on used items. (I'm not suggesting abusing this policy, but do use it if you need to). My pannier-loaded Trek 520 handles exactly like a bike - a big heavy one, but no shimmies, no wagging.
2) packing - think about how you will pack - does your body like the idea of carrying 4 little light bags or 1 big heavy one? Does your body like the idea of kneeling beside the trailer and packing in the items, vs either packing onto the bike (stooping to get into the panniers) or packing the panniers one at a time while either sitting in your tent or panniers on top of the picnic table or kneeling on the ground if you don't have a table.
3) once riding uphill, weight is weight. you have to get it up the hill on the bike or on the trailer. Add up the weight of the trailer and it's bag and compare to the weight of the racks and panniers. It DOES matter which panniers and racks you buy, the choices have very different weights. If you are OK with non-water proof panniers, I would check out Lone Peak (
www.thetouringstore.com) they are a great combination of light weight and good quality. They are not "the best" at anything but they are more than adequate and quite light. I have about 8000 miles of touring on my front ones, and they are doing OK except where a squirrel chewed through one to get to some food. I got some Arkels because the features look so great, and really dislike how heavy they are. I haven't weighed in on Ortliebs, b/c I like side-loading, but not everyone cares about that. A lone peak/light rack combination can come out to maybe 6 pounds lighter than a trailer, and that is totally noticeable. but if you get heavy racks and the biggest Arkel panniers it's about even weight.
Do be very weight conscious of what you pack. This goes for panniers and trailers alike.
4) for the weight calculation, remember you are going to have to carry a different size spare tube (and maybe tire, if you are going somewhere remote, but not in the US) for the trailer. Make sure your trailer and bike tubes use the same valve, or you'll have to switch your pump every time you fill up.
Hope any of this helps...
valygrl