Paying through the nose for Gold and especially Platinum PSU are totally 100% garunteed not worth it (unless you just like having nice shiny posh looking things of course).
Here's some figures I ran the other day for someone who asked me about PSUs. These are two PSU's I actually own and paid full price for as listed.
As you can see - on my representative 500W load test, the Platinum PSU drew 493 watts from the wall, the Bronze PSU drew 527 watts from the wall. Platinum is clearly more efficient than the bronze - it's going to take you a LONG LONG LONG time to ever possibly recoup the extra cost of the Platinum PSU based on your electricity saving of a constant 34 watts.
Make sure you buy PSU's with your eyes open and don't be dragged into the hype.
Butuz