If you're interested, here is a statement from a Maxon developer why Altivec in the Cinema4D renderer gives hardly any speed improvements. Another statement from Maxon is here and here's a general article on Altivec and 3D rendering. The bottom line is that Altivec neither handles 64bit precision floating point numbers nor is it optimized for random memory access (which is essential for ray tracing). Altivec is great for streaming media, e.g. audio processing or video encoding (which Poser handles through Quicktime, and most Quicktime codec are Altivec enhanced). Same goes for the SIMD instructions on x86 like MMX, 3DNow! or ISSE.

As for the lack of OpenGL: I'm with you here, Poser really should be able to use that by now, or better, should be using it since Version 4.