Before I say anything realize that I am nothing more than an anonymous internet poster as is anyone else posting on this board or others so take everything you read with a grain of salt. With that said I have gone through law school myself so I might have some insight, but I could be a crazy homeless person who walked into a public library to post on internet boards about law school fantasies that never happened. I am giving you this disclaimer because I know there is a lot of "stuff" out there for any potential law student and just remember anyone can post anything about any subject on these boards.
With that disclaimer I offer you the following advice. If your really interested in going to law school then you should pick up the fluff classes. Honestly as far as law school admissions are concerned the numbers of your GPA are what matters not the substance. All law schools claim they review the soft factors, difficulty of major, etc. However, when schools are receiving 4,000+ applications they are just going with numbers that is the way it works. I imagine there is an exception out there, but adding a double major won't help your school admissions chances it might hurt them if it is a particularly difficult subject.
However, if your not completely set on law school then a double major may benefit you in your career, life, etc but in the limited arena of law school admissions adding fluff elective courses will likely increase your admissions chances and give you a great deal of scholarship money. While in undergrad I took a lot of flag football, volleyball, etc courses for fun and got A's. I was not intending on planning to law school when doing this, but these activities boosted my GPA and probably played a role in me getting 70,000 in law school merit scholarship money.