While it's true that's a lot of time in Draw, it's also an unexpected amount of time in the "*" (overhead) and "Cull" categories. This might mean something in your geometry is causing Panda to have to Munge it (prepare it for rendering) every frame for some reason. You can drill further into these categories to perhaps gain some insight (is it actually spending significant time in Munge, for instance?).
The reported vertices are fo my "grid" is made of 4356 vertices (33x33x4)
Well, I actually see 0.86K vertices, or 860 vertices, reported on the PStats graph. This means 860 vertices are actually being rendered each frame. Of course this shouldn't be a problem either, but it is more than 128. I assume the remaining vertices are from this other geometry in your scene?
I haven't yet figured out how I can re-direct the ostream from panda
Put "notify-output log.txt" in your Config.prc file, and Panda will dump all its output to log.txt. But I gave you bad advice with render.analyze(); it doesn't exist at the C++ level, you have to create a SceneGraphAnalyzer instead. But no need, just put "show-scene-graph-analyzer-meter 1" in your Config.prc file, and it will be onscreen.
Still, that's probably not necessary; it seems from the PStats output that you don't have runaway vertices or Geoms or anything.
Have you applied any unusual attributes to your geometry like a RenderModeAttrib or something? You're not rendering perspective points? It's not animated?