Some effects have built-in VU meters, like the compressor, maximizer, and I believe the gate as well. I would like if for instance the Delay effect could have a VU meter for the dry, and one for the wet. This thought came to me when using a number of Delays chained for the latest and greatest DDRCompo… Of course a program like Ableton Live copied the DSP system/GUI from Renoise 
(well let’s say it reminds a lot of it…) but there’s one thing they’ve made to rock: there’s a VU meter in between every 2 DSP effects so that you can also monitor with your eyes a little bit what a certain effect/plugin is doing. This is most handy when using VSTs.
Also I vote for more equal D/W sliders… especially in the case of the Delay effect, couldn’t this be just like mpReverb (Dry 0-100% and Wet 0-100%)?
i agree with you on the inconsistency of sliders on devices. some have a single slider, others have dry/wet…
i’m not sure i’d personally use a VU meter on (for example) the delay device though.
I’m not sure it would be useful on all devices, but I would very much want one on the gainer.
I would like meters with numbers of them, especially in the mixer 
Flashing lights on their own don’t tell you that much what they are doing.