Actually, if I understand your post correctly, the specs aren't the same. The Air 2 is running a three-core A8X SoC, while the Mini 4 is running a dual-core A8.
I've kinda lost track of where you started. If you own an Air 1 and are reasonably happy, do nothing. If you own an Air 1 and want a smaller device, either buy the Mini 4 if you want relatively up-to-date hardware or if you want a bargain, buy a Mini 2 refurb or better yet buy my still-under-warranty LNIB Mini 2 and olive brown Smart Case, I'll make you one helluvadeal. If you own an Air 1 and like the larger size but have technolust, you're on your own to make your own decision.
I've kinda lost track of where you started. If you own an Air 1 and are reasonably happy, do nothing. If you own an Air 1 and want a smaller device, either buy the Mini 4 if you want relatively up-to-date hardware or if you want a bargain, buy a Mini 2 refurb or better yet buy my still-under-warranty LNIB Mini 2 and olive brown Smart Case, I'll make you one helluvadeal. If you own an Air 1 and like the larger size but have technolust, you're on your own to make your own decision.