In the future Construct 3 will be faster, so that's a big deal.
There is a comparison list at https://www.construct.net/make-games/new-features
I upgraded to Construct 3 last week, I really didn't need to for my projects because Construct 2 is a solid engine, but there are some features of C3 that I wanted and they are...
Contained animation window. C3 has better dual screen support overall as well.
The admob plugin has reward ads
Improved find function
I should mention how surprised I am that I really enjoy working in the browser.
If you are in the search to earn money from games and you are successful then you will spend a total of $500 for C2, that's currently 5 years of Construct 3. Construct 2 personal is $200 or 2 years of C3. So Construct 3 is worth the try. If you don't like it which I doubt, but lets say you do then you will save $100 by purchasing 1 year of C3.