[Stiglr]

By definition, the more polys and vertices you add, the higher the poly count's going to be. You could save on polys by not triangulating them, but then that depends on your rendering vehicle: some games, for example REQUIRE three-sided polys, so in this case you MUST triangulate, which increases the overal number of polys at least by double.

That being said, you can create poly shapes of cross-sections (as opposed to more vertice-intensive splines) and extrude these, and still end up with a relatively low-poly model. You just have to choose your vertices carefully, make use of smoothing, and model with a low poly count in mind. That involves making decisions about smaller details: which do you model in 3D and which can be cleverly done in texturing?

If you're working on an aircraft, I've done a series of video tutorials where I use extrusion techniques for low poly models (and those that require triangulation, to boot). Perhaps they'll help you. Find the link to these in the Tutorial section of this board.