I am sure that (just like everything else) some composers are very aware of our instruments potential, while some (probably a higher percentage) are not.
Is there enough music for the tuba? Well, probably not, but it does get better every year and really, that is about all you can ask for.
What's the solution? I would suggest that rather than waiting for new composers and compositions to discover the tuba and tuba players, that tuba players instead discover composition. No-one has a better idea of the possiblilities for this instrument than those who play it. If everyone of us would find an hour a week (yeah, I know...they're hard to come by) and attempt to create a few bars of cool tubaistic (a perfectly cromulent word) material, we might find that we have the compositional power to change the situation.