if your using an assist card just go flat out alch rather then use your money on a player card. now if you are willing to use your money to do so just use it for another character rather then a re birth. alch is quite powerful only if you can spend a few hours grinding the skills needed to get some great results. personally i would rather go with vates for battle alch, transmutation alch, and warrior. but i would only do that on a elite or hero card due to the fact that it gives me decent stats.
http://wiki.mabinogiworld.com/view/Talent/Hero_Talent_Tables#Night_Sage