I also saw something along a similar vein I believe in a FB post. It mentioned small groups or bible studies, but in a way that brought out some of the "so called" bad things that can happen and then made the point that taking the time to plan, go to such studies or groups, really didn't mean anything if other things were off balance or lacking spiritually.
On the surface, both of these points would seem to be good indicators of whether or not someone was truly serving the Lord in love and truth and not just out of "duty", but I simply can't find chapter or verse for this. What I can find, is that love seems to be shown best, when we go against our own selfishness and desires and yes, even out of a since of duty, do what the Lord commands of us. Feelings may be there some days and on other days, they may not. Doesn't change anything does it? Does the bible teach us to "be emotionally in love with God" or just to love Him because He is God and commands us to trust and believe in Him?
Much more I can say, but we must be careful either way. I understand the warnings and the points, but if we start judging who is serving the Lord or not by their emotional response and or motivation, we may have left the scriptures and entered into man's way of judgment. Many things effect how we feel, but what is at our core matters the most. This isn't to say these things should not be questioned, but each case will have its own merits or faults and lumping every unmotivated non emotional Christian into a category, is not the best approach.