I also have a previous BA. Here's what I've been told regarding a previous degree: You do have to obtain a BSN to get your Master's in Nursing; a previous baccalaureate degree in another field won't suffice. I do not think an employer would necessarily care if a potential employee had a previous degree besides nursing ... although it certainly doesn't HURT!
I don't think it's "better" to go for the BSN ... UNLESS you want to further your career and education in Nursing (for example, move into a higher administrative position or pursue something like a CRNA). However, I've been told by other nurses that there have been people that they worked with who had a previous degree and an ASN, and that they moved into administrative positions within the hospital ... so I definitely DO think a previous degree is an asset to some degree, no doubt.
It's good to keep in mind that someone with an ASN will make the same salary as someone with a BSN ... It's just that, if you want to further your education or career in certain areas of administration, you need the BSN. Also, you CAN be a Charge Nurse with an ASN. My brother-in-law has an ASN and has been a charge nurse for year ... in fact, he gets calls from competing hospitals offering him bonuses to come work for them ... again, he has an ASN, not BSN.
One other thing about having a previous degree -- I don't know about your college, but one of the factors that my school looks at when considering someone for acception into clinicals is whether or not they have a previous baccalaureate degree and how well they did in that degree ... I think it is just a testiment that a person can start something and finish it successfully ... which is good when they are considering someone for clinicals!
Anyway, hope this helps!