While 12's "can" be handheld your 10s are going to be way better for that purpose and 8s better still. Getting a consistent clear image freehand with 12s can be challenging. Can you give us some info on what you're wanting/needing the extra magnification for? Western hunting, Field use in the midwest, neighbor kid's girlfriend, etc? Do you regularly use a tripod? I would never recommend 12s as a one-and-done bino and likely not at that price point but if you are keeping the 8's, 8+12 is a common split for folks who own several binos.
In all honesty if you're thinking of investing your hard earned dollars in changing up your glass, you would very likely see a more significant impact by jumping up a tier or two in glass quality than you would see jumping up in magnification. Hawke Frontier ED, Meopta MeoPro, Maven C1s, Athlon Cronus would be the next logical place to look I would think.