I wrote up a bigger post, but I felt like I was going on a tangent.
I think a large part of the reason why people don't get reactions is heels simply failing to generate heat. If they aren't doing things that make people dislike them then they won't get booed and people won't tune in to finally see when they get what they had coming to them. Now I'm not saying heel's should be booed for every single they do, but their job shouldn't be to win the crowd to their side. A heel should be taunting, mocking, calculating(working a bodypart for example) and sure they could be prideful and bust out a cool move, but only at the right times like when they believe they have the upperhand. It makes no sense for them to try and win the crowd over because that's the faces job. I know you feel there should be shades of grey, but that's only really effective at the right times. See: Shield vs The Wyatts.
Sadly, I think the only real "heat" you can generate with the modern "smart" fan is being perceived as not worthy of their presence based on perceived merit and ability (e.g. Eva Marie, Roman Reigns). I'm open to counter examples, but I can't think of any.
I'm personally at the point where a well-written, well-performed baddie can be appreciated on those merits. I don't perceive there ever being a time where it's so well done that it achieves its intention. I mean, it's a lot like the admiration for a performance in film this point, but just not as good.