HDR questions

You need to add an env_tonemap_controller and send it inputs from a logic_auto to keep the HDR in check (should prevent the overbrightening and whiteness you have). See here for more: http://developer.valvesoftware.com/wiki/HDR_Lighting_Settings

Also, pretty much everyone uses HDR for later development releases, it's a standard now.

I would say that there is no reason for HDR in alpha, but once you get into late beta, and are finishing up your detailing is the time to add it.