You're far more likely to get bored with a bike that can't be ridden to its full potential. I've owned a number of touring bikes (Goldwing, 1200GS, Harley Road Glide) but only used them for commuting. They were being wasted in the capacity. I've owned two CBR600RRs - excellent track bikes but a not at all fun to ride in stop and go traffic and their handling and performance capabilities can't be (legally) taken advantage of on a public road.
On the other hand, the CBR250 is a user friendly bike that inspires confidence -even with newer riders and yet on a public road, will handle (if not out-accelerate) pretty much any cage - and you'll have fun doing it. And even if you get bored, look at the going prices of used Ninja 250s and you'll see that the CBR stands a good chance of maintaining decent resale value - so it's a win/win.
There's a lot of truth in the old saying, "It's more fun to ride a slow bike fast than a fast bike slow."
Disclaimer: I've test ridden the CBR but I do not currently own on. Yet.