I want to create an overbloom effect on an object by manipulating its materials.  It's not really specularity though as the item in question is not lit and instead has ambient light.  What I'm trying to simulate is the illumination of many tiny lights on the outside of a large ship.  Setting the ambient color and value will ensure each light is visible in the dark, but it's rather dead looking, hence the desire to have a glow or overblooming.

Any ideas?

Depends on which version of Poser you have.

Poser 8 and Poser Pro 2010 have Indirect Lighting which might suffice to get that effect.

Poser 7 or lower would require using an image editor to postwork the effect in.

The other alternative in P7 is to use a gather node in your material receiving the emitted light.  Here is, at least, one post about it; there are several other post throughtout the forum.

http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2816103

As modus0 mentions, IDL in P8 and PP2010 creates a better affect.

This is in PP2010.  Beyond checking IDL in the render settings is there anything else I should be considering?

Depending how small/large your material light source is. you may need to adjust the ambient value to something greater than one.  I have seen values up to 10 or more.

They are pretty small lights (port holes really) so what I'm likely going to end up doing is just using photoshop to select the light's color, which is unique to the rest of the composition, copy to a new layer, and blur for effect.  That'll give me my glow simply enough.

That sounds reasonable.