Flight idle on B737 Classic ( and I seem to remember also on NG) always gives you more than 30%N1 through Flight Idle. ( thrust does not increase with EAI ON by the way) Only if for one reason or another you have Ground Idle ( MEC/EEC related mostly), there is a chance that you will get a bright blue EAI light, indicating a valve that is not in its correct position. I have seen this in operation indeed, but only on a couple of occasions during my 14 years on B737.
It is more prevalent during ground operations.