I think a lot of it (straps vs no straps) is about what you are used to.
In the right (or very wrong) snow conditions, a nordic skier might be 100 percent propelled by their poles. 20km and 30km World Cup Races have been won by people double poling the entire distance. Ouch.
Probably more typical for a nordic skier on groomed trails is twenty to thirty percent of their propulsion coming through the poles. Skating in the backcountry on solid morning snow is probably comparable. If you are breaking trail with a heavy pack and shuffling along you probably are only getting ten or fifteen percent of your forward momentum from your poles. And you won't be doing much double poling with a pack on.
Skis are supposed to slide. Walking shoes aren't supposed to. I'd guess those simple facts put an extremely low upper limit on how much power you could get through poles. Probably five percent under optimum karma.
I don't think anyone has worked out the mechanics of using trekking poles for walking as well as how nordic ski racers use poles for, well, racing. All we really have to go on is anecdotal evidence and our own personal experiences.
I love straps. I can scramble over a short section while letting my poles dangle and not get too tangled up. I can also stop and eat a clif bar while walking (or skating) without too much awkwardness and not worry about forgetting the pole when I move on. I don't think I use my poles very much for propulsion, but a lot for balance, especially up or down steep hills.
What gets me about this whole exercise is that you can buy a pole for less than eighty bucks at REI that is cheaper and lighter than non-adjustable hiking poles from several manufacturers. And I don't see any technical reasons that should be so. Even more interesting, such poles are quite common. A lot of outdoor stores that rent skating skis would have poles just like those. You could probably buy a used pair for fifteen bucks. You could probably find two broken poles that you could salvage as walking poles for free.
It seems to me that you could swipe the basket part from a busted old pair of adjustable poles, cut the ski poles down to an appropriate length (for me, from 150+cm to 120cm) and have a super-light frankenpole. The major out-of-pocket cost would probably be for the epoxy, or maybe a hacksaw blade too.
Doug, yes, the basket assembly on a trekking pole, at 1.0 oz per pair, is most definitely heavier than on a nordic pole. But the weight on REI's web site was for a 155cm pole! I typically adjust my trekking poles around 120cm. I'd bet that 35cm of that example pole and the lightweight basket weighs *more* than the basket assembly on a lightweight trekking pole. So you'd still end up lighter.
Hopefully someone who makes ultralight trekking poles is reading this and getting some ideas…
Oh, and I love excel poles. Too bad that they are almost impossible to get in the states anymore. I heard they went out of business.