Back on topic, all of this is pointless, because device with limits 500-900 (or any other) doesn't "sit" on 500 when idle - it effectively underclock to 0 mhz, so You save also on power leakage. Talking in simplified way, CPU do it's job, and then go to "sleep" - every second.

So, if You set limits to lower (i.e 250), You got less time on 0 mhz - every second - cause it takes longer to finish "idle" set of task on 250, than on - for example - 500 mhz.

Furthermore, monitoring every dbus signal use resources and battery power.

Effect is, that You loose battery life, instead of gaining it. Of course people will report increased battery life - via placebo effect - but there is no reason why it should give any real-life gain.