Mars certainly plays a part in stabilizing the asteroid belt.
I’ve read that its believed that Mercury will one day fall into resonance with Jupiter and be slowly pulled outward from its orbit.
Besides, mars is already in the habitable zone around our sun. Its problem isn’t a lack of solar heat but an inability to hold it.
One idea is to direct asteroids into Mars adding to it's atmosphere as they burn up gradually increasing the air pressure. But then the calculation is if Mars is big enough to sustain a viable atmosphere.