1) Any engineering degree is useful. You don't necessarily need a degree in a specific field in order to get a job in it. You need experience and know-how primarily.
2) If you want to be an aeronautical engineer, then a degree in aeronautical engineering is pretty darn useful, no?
3) Do you know what aeronautical engineering really is? You don't design planes. Groups of people design planes, AE's do flow calcs for propulsion systems, Boundary layer calcs for surfaces and body shapes, turbulence, aerodynamics, etc. Aeronautical engineering is heavy on calculations and simulations. That is not to say that you are not an integral part of the design process, but you won't be so involved in the actual mechanics and engineering of the thing so much as the shape of it.
4) Generally, schools offer dual degrees in Aeronautical and Mechanical engineering. If you want to get into the mechanical side of things, this is the way to go. Especially since there are many more jobs out there for MechE's than there are for AeroE's.
5) Also, if you do decide to stick with the aero side of things, you might consider higher level education. Aerodynamicists benefit greatly from masters degrees.