I gave my 3rd gen iPad to my wife because I like my mini so much. I don’t think that’s a stupid move at all as long as you can reasonably afford it. Heck, some people keep both since the larger iPad does have its advantages.
As for selling an engraved i-device, I haven’t had much experience with that. I flipped my share of devices back in the day, but none were engraved. I bet you could put it up on Craigslist or eBay, or maybe even try Gazelle, and get a decent price for it despite the engraving as long as you’re up front about it. Most people just wrap their iPads in a case or put stickers all over them anyway, so the engraving might never really be seen. Try mentioning that in the description—the right buyer might simply not care and you could still get some decent money for it.