A lot of people find success in specializing the band members to different skills. This is because the better the skill, the easier it is to maintain it and get successes. So for your writer char they will churn out songs really fast and you'll end up with more than you know what to do with! For the band score during gigs, your band's TOTAL scores are weighed rather than the individuals themselves. So this strat does work.
Buying gear at the shop helps ensure that band members never drop below a certain # in the respective skill. So buying a guitar means that Dallas can't bottom out on his music skill anymore, so you can focus him on other things if you need to. That bonus to his skill counts as actual skill. Buying gifts at the mall will also reduce their stress and raise their affection.
It takes a while to get a good song writer in your band but it's worth the investment. Pick someone you think would write songs in the vein that you want for your band (angry Robin, sexy Beau, angsty Dallas, or silly Emmitt)
Good luck!