Surely you don't need me to list all of the pracical benefits and applications of gravitational theory? Do you realize just how much of physics has its foundations in gravity? I don't think this is a good example for your argument. Also: anti-gravity has been researched - I even recall some Russian scientist claiming he can slightly descrease gravity. It has massive potential benefits if it is possible. Space travel/colonization (and complete space dominance) being one of them.
Your second example, the Big Bang, is a better example. However, I, as a layman, could name many practical applications that arise from studying the proposed "bang" origin of the universe. First and foremost: a better understanding of physics. Perhaps even a unification theory for Quantum and Newtonian physics, which we lack. Gains such as these may give us our replacement to nuclear energy. Or, as you stated, an anti-gravity device. I will admit that these are obviously "down the road" benefits to a theory that may never be validated. But many such prior endeavors have lead to some incredible gains. Thus scientists pursue some things they know may never be fully understood.
Intelligent Design, as far as I can tell, does not offer this. Intelligent Design begins and ends with God, who is above the realm of man and science.
You seem to be saying that even if life is intelligently designed, that fact is irrelevant to science. Frankly, I am baffled that anyone could seriously entertain such a notion.
The main objective of science is to understand nature. The question of whether it is intelligently designed is certainly significant. If it weren’t, naturalists would not go apoplectic over the notion that it is.
Suppose space aliens land on earth and find a old junk car that was abandoned out in the desert. They decide to study it to determine all they can about it. Do you suppose they would be interested in knowing whether it was designed or whether it came together by some unguided process?
Gravity took centuries to get from Copernicus to our present state of confusion. Nevertheless, our understanding is useful, if incomplete.
The more we learn about the minimal states of life, the more likely we are to be able to treat and prevent cancer and genetic disorders.
At the moment, tens of thousands of home PCs, including some owned by freepers, are working on understanding protein folding.