I don't blame you for this feeling. It's not completely unjustified, but I'll add my arguments for the scanner, just so the full story is told.
Passcode Security: It's always tempting to let security slide on an iPad or laptop. It's a pain to enter a password or even a passcode ever time you pick up the device. From what I'm seeing (both from myself and from what I hear other's say), Touch ID convinces people who used nothing to use passcode, and people who settled for a 4 digit passcode to use a full password. I'm in the second camp.
Web Security: 1Password and many other password apps now work directly in Safari and several third party browsers. This makes it easy to use longer, more complex passwords for your various website accounts. More importantly, it lets you easily use a different password for every site. In today's online world it's very risky to use the same password everywhere. All it takes is one security breach and your accounts can fall like a row of dominos.
Pure convenience. If you use a passcode or password it takes three steps to unlock your iPad: Tap the home button, swipe the screen, enter your passcode. If you forgo the security (for whatever reason) it's still two steps. Touch ID reduces this to one step (except after a restart) Press the home button, and leave your finger there for about half a second.
And some other minor reasons, like quicker purchases in some apps and the App & iTunes Stores themselves.
It's really hard to explain how Touch ID changes things. Before you have it, it seems like a trivial feature. After you have it you'll miss it on every other device you own. I still catch myself pressing the home button on my iPad and waiting for it to unlock, before I remember that I've only got that 'trivial' feature on my iPhone.
That 'all' said, I'm not really trying to talk you into getting the iPad Mini 3. I just want you to understand that while the feature may not be worth an extra $100 for any particular use or person, the feature itself is by no means a ripoff. It's a powerful and game changing tool. It's the future of every mobile device.
Ok, I'll stop now.