What does the Mini 3 (non +) have that the Mini 2 doesn’t?
Larger screen,
touchscreen (can be disabled, also operable via buttons only),
color display,
base map,
text input via touch possible,
various keyboards for text input,
satellite setting for “all + multiband”,
Garmin Share
IPX 67
What does the Mini 3+ have that the Mini 3 doesn’t?
send (via mess app)/receive photos/forward received pics via M3+
voice messages
voice notes
siren
text messages up to 1600 characters (Mini 3 (and Mini 2) only up to 160)
more free memory
As an aside: 3 out of 4 consumer plans already include a number of photos/voice messages (10/25/50 per month), which you can’t use on a Mini 3 non plus (or a Mini 2).
Of course the current Mini 2 sale price ($/€ 249) is a really good offer. But for a more up to date device, I would go for a Mini 3+, especially because the price difference M3+ ($/€ 499) : M3 ($/€ 449) is only 50$/€ (side note: the M3+ comes within carabiner loop ($/€ 15), which even makes the difference less).
I have chosen the M3+, but that’s only my opinion. I have upgraded my Mini 2 and for me it is really a big step forward (but the Mini 2 is still a good device!). Perhaps this post helps someone. But people may see it different. This is only intended to be a possible aid in the decision-making process.
I haven’t mentioned Messenger/Messenger+ because the display is too small (my opinion) and for a comfortable use you will need the Messenger app/phone ( also my opinion). Mini2 and M3/M3+ are more useful for standalone use.