Dolby ProLogic IIz, DTS Neo:X and Audyssey DSX processing will extract audio cues from the other channels and redirect them to the height speakers, much like how traditional ProLogic extracts a center channel from 2-channel sources. Ideally, the only audio coming from the height speakers should be ambient effects such as wind and rain, or the occasional discrete sound like a helicopter passing overhead. You don't want dialogue coming from the ceiling.
Just some additional remarks on this: Dolby IIz and DSX generate the heights content - in case of DSX also wides - artificially, by using algorithms to generate the signals from the other channels.
For DTS Neo:X there are two BDs -Expendables 2 and Dredd, I know of - containing so called DTS HD 7.1 tracks optimized for DTS Neo:X 11.1. There are discrete tracks on these disks, muxed or matrixed in the L/R and SL/SR channels.
Every player can play this and hand it over as bit-stream to the AVR. But this must have Neo:X for decoding and the necessary outputs - 9.1 or 11.1.
crussader, you will never hear these tracks in your setup, but I believe you are aware of this. My opinion is do it, and if you like it, keep it, why not. gsr described the drawbacks clearly.