Hey, the question was all yours, Drhorsepower, and it's a good one.
I use ultralight backpacking gear when backcountry hunting, but my optics are a bit big.  It is worth it to me, because there is a noticeable difference in low light performance.  Right now, I backpack with my Swaro SLCneu 10X42s, A bushy Elite 1500 rangefinder, and a Vortex Razor 85HD spotting scope.  I like to digiscope and videoscope animals through my spotter while hunting and the Razor's large objective is definitely a benefit.  It is about a pound heavier than most 65mm spotters, and I make up that weight in savings on other backpacking gear.
However, I am considering adding a nice 50mm spotter to my collection for fast and light hunts.  The Nikon ED50 is the best I have used, but it doesn't have great eye relief.  I also like the Minox MD50, and it can be found for a bargain, but no ED glass.  I noticed that the Vortex Viper HD scopes have eyepieces that are labelled for magnification for not only the 80mm and 65mm Viper HD spotters, but also a 50mm version!  While I haven't heard an announcement, it sounds like a 50mm Viper HD is in the works, and I am anxious to see it.  It might make a nice compliment to my Razor HD.
I will stick with full-size binoculars, because the weight is worth the performance, given how much time I use them.  A good bino-harness really makes the weight bearable.  I hardly notice the SLCs, and they certainly aren't lightweights.
I am interested to hear some other replies.