I have an associate's too and have been struggling with this as well. Most of the RN-MSN programs do not offer a BSN... this is not a problem if you finish. If you don't finish, or quit part way through you are back to just having your RN. I have chosen an RN-MSN program for NP and it does not offer a BSN. This saves a lot of money because it cuts down on a lot of courses I would have to take if I did my BSN first. I have no desire to get my BSN to have my BSN. It would merely be a stepping stone to the MSN. If you can get through the whole program without having to quit, this would a great option. But if you anticipate something like having a baby or what not during the program, you may be better off getting the BSN. There are also some RN-MSN programs that do award a BSN as well... I have no reason why I would need to quit, and if something were to happen, I have looked at their LOA policy and it satisfied me, so once I do it, I am going all the way. That was another benefit to the RN-MSN... by not getting my BSN first, I don't have the chance to "take a break" and then have it be years down the road before I actually go on to graduate school.
It is purely a personal choice, but if MSN is your goal, go for it! Don't waste the time on your BSN.