What does -spec_exp, -spec_tube, -spec_point and -spec_static ?
-spec_exp does nothing for the most part. It only applies to non-HTL mode, which pretty much no one uses. The default value is 16.0.
-spec_tube applies to tube lights, basically just beams (but I'm going to try and make warp effects use it too, for the coolness factor). The RGB values for the specular of that light are multiplied by this value. The default value is 1.0.
-spec_point is just like -spec_tube, except that it applies to point lights (weapons fire, explosions, warp effect, etc.). The default value is also 1.0.
-spec_static is just like tube and point, but applies to static lights (suns, techroom, etc.). Like the other two, the default value is 1.0.
So, for -spec_tube, -spec_point and -spec_static, values less than 1.0 will reduce the amount of specular from that light and values greater than 1.0 will increase the amount of specular from that light. And note that all of this only applies to the specular portion of the lights, not the overall light brightness. Also take note of the fact that nowhere is the current code does the RGB values for specular on point or tube lights get set. And the default value is 0, which means that currently, neither -spec_point nor -spec_tube actually do anything.

However, -spec_static does have a default value of 1.0, so of all of the options it's the only one which actually makes a difference in the game.
Personally, I use a -spec_static value of 1.5, -no_emissive_light, and an -ogl_spec value of 60. I tend not to change the default ambient light setting though, that all depends on the particular mod. The -ogl_spec value changes the basic shininess of the specular light in OpenGL. A lower value reduces the overall intensity of the light making it broader and less powerful. A higher value makes it more focued and brighter. The default value is 80, and the usable range is 0 to 128 (clamped). The original default value was 60, which is why I still use that, but many people seemed to think that 80 or so was more "D3D" of it.