I think this is something we all need to petition DAZ about; Carrara desperately needs specular/diffuse settings on all its lights. Seriously, this is an industry-standard feature that even Poser and Daz Studio offer! There are countless everyday lighting approaches that require specular/diffuse lights and you can't do 'em in Carrara without a lot of messing around.
That being said, Shaders Plus is your best bet. Lighting Control and Selective lighting are 2 things I can't live without!
JT