Before we can determine what the difference between being imaginative in science and pseudoscience is, we have to determine what the difference between science and pseudoscience is. The aim of science is to challenge claims that are made as well as look for evidence that might prove the claims wrong. Pseudoscience is the opposite. It looks for evidence to support the claims that are made.
There is no need to be imaginative in science. The data speaks for itself. Pseudoscience is, again, the opposite of science. It is sometimes necessary for one to be imaginative to draw conclusions in pseudoscience.