Forgive me if some of my points regarding Lavos in CC are a little off, as it was never released in Australia.
Lavos came to Earth probably based on pure luck. However the whole thing that it takes ages for him to gain power, I personally feel is wrong. When he crashed into Earth, he triggered the Ice Age, since many creatures died during this and many struggled to survive, it would have been difficult to gather power. Then of course, his energy was drained, making him have to gather more. I would say that roughly, it would only take from 12000 BC to 1999 AD to get to full power.
My view on why Lavos never really detected Chrono and Co. whilst they were slowly getting closer to destroying him, was because he was nothing but a parasite. He only became 'smart' when he merged with Schala in the events of CC.
The main thing that I am trying to empasize is the fact that in CT, Lavos was nothing but a mosquito or flea - doing what needs to be done to survive. It was only until it was in the Darkness Beyond Time with Schala, was it able to observe her, and in a way 'evolve' into a greater being that it merged with Schala, and had a human mind at his disposal.
What do you think about this?