Is a second bachelors degree worth it? I'm about to finish up a BA in linguistics and am looking at some interdisciplinary options for grad school (specifically in cognitive science). 

I have a competitive GPA in my last two academic years, though my first year was a bit of a wash to say the least. 

I was thinking that it would be a good idea to go back for a second degree for the following reasons:


to boost my cumulative gpa (my academic performance in first year was a pretty big blow to my cgpa)
to gain a better understanding of my research interests. (There are certain science courses that I haven't taken that make me feel downright incompetent without, such as first year physics and math.)


However, I'm acutely aware that I know nothing when it comes to grad school admissions, especially when it comes to interdisciplinary programs such as cognitive science. Is a second degree worth it?
Unless you have in mind a second degree in a completely different field, I think you'd be spinning your wheels.  You can probably take those physics and math courses in post-baccalaureate status; check with the institution from which you got your degree.

If you are thinking of a second bachelor's degree in a field similar to your first, go for the master's degree in that field instead.  Your freshman year GPA will probably not keep you out of most programs since you have a solid record in your final years.  Presumably you'd get good recommendations from your upper division professors.