I doubt you'd see much difference going to a 12x from the Night Owl. I have a 10x56FL and a 12x50 Nikon SE and one will realistically to what the other will do, in terms of resolution. The fov of the Z seems ever so slightly wider and it's a tad brighter, but that's about it. At 15x, the magnification difference is more noticeable, but to be of value, the quality of the bino must equal the 10 or 12 level, whatever the particular units being compared is, and ya gotta be able to hold it relatively still....no meat feat w/o a tripod or IS. The 15x50 Canon fits the bill on that, and is excellent optically, giving up very little to the Z or the Nikon. The 15x56 Swaro has a (very) slight edge optically, but is harder to hold steady, even if the Canon's IS is off. Both are what a seemingly huge majority of birders would consider "heavy"....a few oz less than the Night Owl, but well over 40oz.
You have now one of the best 10x ever made, and I seriously doubt you'd gain any performance edge going to another glass. A change would likely be a letdown.