I've never noticed much of a change in CPU, mobo or graphics temperature from those things.
I can see the point made by AigoMorla and others. In fact, two years ago, or maybe it was three -- I was saying that I thought all the bling-bling was silly. Then I started using some Logisys(?) blue LED "strings" each containing 16 or so LEDs-- using something like 0.02A of 12V for each string.
My tastes are a bit more sophisticated with my latest case-build. Except for the faint-white LEDs on some case-bottom Aerocool "Silver-Lightnings" (which may get replaced with non-LED fans like Sharkoons), I've installed the Logisys CCFL "rings" on a center-case fan, and the switch for it in the case-chassis near my power-on/off toggle-switch. I've used Mylar film to "mirror" my side-panel window. So the innards are nearly invisible but for the mobo lights and those bottom-fans (which are faint LEDs, anyway), and if I flip the switch to the CCFL, I can see how much dust is accumulating in the case, or otherwise tittilate people who go goo-gah about the lights.
Since I'm ambivalent about lights, this arrangement comes closer to something I can live with all the time. It's all "switched." The side-panel looks like chrome or a mirror until I flip the lights on.