You can use every single different Idol for every single different spell you cast without causing any sort of GCD delay.

#showtooltip Moonfire
/cast moonfire
/equip Idol of the Unseen Moon

#showtooltip Starfire
/cast Starfire
/equip Ivory Idol of the Moongoddess

#showtooltip Wrath
/cast Wrath
/equip Idol of the Avenger

Copy and Paste these macros for pve moonkin pwnage.

Even with the inc nerf to the Idol of the Unseen Moon these macros still provide a nice dps boost.

When the Idol of the Unseen Moon does proc and then you cast a starfire/wrath afterwards you get the bonus from the proc and the bonus from the starfire/wrath idol.

Note: If you are out of range of your target and press the macro it will incur a GCD without casting the spell so I do not use these for pvp

I would also recommend an addon called "Quartz" for monitoring your spell casts / GCD's and latency