Def. save up for the cassis Passy! I tend to want to do those things too, ie. buying an accessory or something small while saving up and waiting to buy my dream bag. But my DH keeps reminding me to wait and get my dream bag in the end!
You should save for the bag, you will use it more often. Do you have a birthday or anniversary coming up? Valentine's Day is just 2 days away...you could ask for a GC for LV or cash so that you can save for both the bag and cosmetic case? Just a thought.
Accessories are tempting for me.. but when theres a bag that i like..i put the accessories on hold and buy the bag..then go back to it later!
So save for the passy..very pretty!