Recently switched from guitar to bass (Still play guitar everyday) due to the new band and my ever growing fondness of the bass. From years of playing guitar and the bass every so often I'm not bad, can play alot but my main problem is writing, it seems a bit bleak and dull to what could actually be hip and exciting. Having learnt many songs I know a few extra notes from memory but not half as much of what I should.
Should I be learning scales and if so which ones?
Learning scales will help, no doubt about that. However I suggest that you learn chords, seeing as how you are a guitarist I assume you already know at least a few. Use these chords to help you work around the root note. For example, if you are playing a section where you a just playing root notes, use the notes in that chord to throw in some fills and make it sound "interesting". And like I said before, the scales will help, so learn those too.
So that with good courage we say, “The Lord is my helper. I will not fear. What can man do to me?”

-Hebrews 13:6