Pure theory is like exploring the universe by staying on Earth. Sure, it seems expensive at first to build space ships, but our brains are at their best when facing reality up close. Too many scientists work exclusively over models in their mind. Then they are surprised that nobody outside their clique finds what they do interesting.
And I am not thinking about Mathematics: Mathematics was founded by people who wanted to sell land by area, not perimeter… modern Mathematics came to be with Newton, who wanted to help the state manage its money better. I am thinking about Software Engineering researchers who never write software and never study people who write software. I am thinking about Semantic Web researchers who have been building models and ontologies for ten years, but who have never tested their ideas against the harsh reality. I am thinking about Algorithm Design people who claim one algorithm is better than another, but they never bothered to implement it. I am thinking about Machine Learning researchers who never bother to test their schemes with the terabytes of data we find everywhere.
All topics warrant research, but pure theory is not an acceptable methodology.
It doesn’t matter how beautiful your theory is, it doesn’t matter how smart you are. If it doesn’t agree with experiment, it’s wrong. (Attributed to Feynman)