Edit: Normally I label the overly technical posts as being for a target audience, but I did not this time. My bad -- this post is really only of interest (and will only make sense) to serious 3-d modelers - the advanced airplane and scenery nerds!
The brightness of specular hilights is out of sync between HDR and non-HDR mode in X-Plane 10.11. This wasn't intentional - it's a bug. 10.20 will fix this; specualr hilights will have the brightness you see in non-HDR mode (which we think is more like they were supposed to work*) but the tinting of HDR mode (non-HDR mode was overly red in 10.11).
I get a lot of requests for 'hardness' control - that is, the exponent that controls how wide a specular hilight is. We'll get this feature eventually - it's too important to ignore. The main delay in having this feature is that X-Plane uses a deferred renderer, so the specular exponent has to be stored in the G-Buffer somewhere, and storage is tight.
For similar reasons, it is very very unlikely that we'll ever have RGB tinting of specular hilights. Doing so is 3x as expensive in G-Buffer storage, and we need that storage for other features.
* That is, unless we discover that non-HDR mode looks spectacularly bad in some cases, in which case we may have to push things a little more toward how HDR was.