It has no negative effect I can discern. I too have started adding the DME after steeping simply to avoid boil overs, to which I had my first adding DME to a boil two batches ago - what a mess. I don't think the DME helps bring the wort to a boil quicker, but I guess it might be possible since a denser wort would probably transmit heat more thoroughly, going on the premise that lighter materials are better insulators. So I don't know exactly to be honest. But nah, I wouldn't worry about any adverse effect, at least I haven't seen any yet.
BTW, 180 is a bit high for steeping. Most do somewhere around 160. It's said anything past 170 and you risk extracting tannins.