If you have a fresh installation of a sybase-server, it can't hurt to update to a higher EBF. Application generally specify which version of a database can or cannot be used. If your applicatie specifies ASE 12.5, you probably can upgrade to the latest EBF for 12.5.
When you have a working environment and you don't have any errors, I personally would not upgrade just because there is a new EBF. If it isnt broken, don't try to fix it. If you wantto upgrade anyway, test it thoroughly.
I'm not crazy, I'm an aeroplane!