Leaving the price aside, since it has already been discussed many times, I think that the real problem of Construct is their use base itself.
The way majority of games published with Construct are silly mobile or browser games, and that's what someone that hear about Construct sees. If I am using a different engine or I never programmed and I want to develop my big dream game, I will not be interested in an engine that mostly create endless clicking games or clone of other simple games like Flappy Bird.
I've been using Construct since 10 years now, and I am still amazed about what I can bring it out from it, and not only from C3, I still keep using C2 for many of my projects too and it's still great!
Yes, a new user will never end up in creating their MMORPG with Construct, but they will never do it either with any other engine, because they lack of experience more than it be an engine limitation. So, you need to show well what can be achieved if you stick with Construct at the very beginning of your page. The rotating cube is nice, but if you don't keep looking at it, you can really see the good games like The Next Penelope or Mighty Goose. I think a slideshow underneath it, if you want to keep the cube, of other good looking games is good to have, especially if you can click and see 1-2 minutes of gameplay.
I think you can also include some of the games done with C2, in the end you can say "If this was achieved with C2, can you imagine what you can make with C3?".
There a few games that are graphically astonishing, and since we know that the eye wants its part, I would add those at the very beginning of the homepage. Videos of games like Remote Life, Cyber Shadow and Klang will make a huge difference. These are published games on Steam, so new users can see what is achievable completing a game with Construct.