I suspect the warning about combining that product with MAOI's may have more to do with he fact it contains 5-htp than there being any kind of potentiation of the actives in the calea. MAOI + sero precursor = sero syndrome.
Regarding some people not getting effects, with calea I've found most people need to take it for multiple nights in a row before they start getting dream enhancement effects. Most people start getting it by the second or third night, but I've seen cases where people had to take it nightly for up to a week before they got any effects.
I have used calea with harmalas and dmt pretty extensively in changa blends. I do find the calea seems to help a bit with lucidity within the experience and aides in recall when returning in much the same way it does with dreams. It may not be the tastiest additive but it's certainly effective in this regard. I haven't experimented with utilizing oral calea with ayahuasca yet, but I suspect it would have much the same effect it does when smoalked in changa.
If you are big on the oneirogens you should look into Silene capensis and Synaptolepis kirkii as well.