I am somewhat bemused at how this thread has altered course.The OP just suggested adding new colours for the golf bags with just cause. However it has digressed into whether or not they are a waste of credits.
Many would say buying clubs and balls is also a waste so it comes down to what you want. If a virtual bag that does nothing but sit there makes the purchaser happy, then IMO is it well spent. But it is a choice, no-one is forcing anyone to buy a bag, avatar or even balls or clubs.
We do it because we love the game and I find it somewhat judgemental to base your opinions if that person is wasting credits regardless on whether or not someone elected to buy a bag.
Looking at many players profiles the bags have been a commercial success for WGT so there is no right or wrong, just a choice.