If you are a recruited athlete, I think that you will need to apply ED, and if you are not, ED may not offer much of a boost in admissions.
So the choice is not whether you should apply ED for a minor boost or not, but whether you should apply as a recruited athlete for a major boost.
That being said, Grinnell will not offer more financial aid than most of the NE colleges. Colby, for example, will offer better aid. You need to run the colleges EFC calculators to get a better idea. What Grinnell will offer, as a recruited athlete, is one of the best chances you have at admissions to a college with low acceptance rates.
However, you could also get recruited as an athlete to other colleges.