Base does tend to be used to simply enhance the music, and that is a very important role - although simplistic, yet very-very important. I've read some quotes here where it mentions about baroque music, where mainly two lines (one base and one alto or tenor), work independently to create a melody. It is possible and there are many bands that I've heard doing so, however, they do it only in some parts of the music.
I studied music own my own for a few years and played guitar for many years. I am no master by no means, but my thoughts are that base is difficult to hear even when it is doing a lot of work, perhaps because of the over empowering sounds of all the other instruments playing at the same time with higher notes. I do agree that there is a lot more that composers can do to give the base more justice. I've created a few compositions and one of my rules is to mix the base: Keep with the root for some time, and in other parts where required to enhance the music, have it do something else to create a variation, but I don't like to make the base different all the time. I guess I could compare it with a guitar...Everybody likes to hear a solo, but if you do it throught out the whole song, in all of your songs, it might not sound that great. A good mixture is my preference.