I suppose it all depends on the details of the cockpit. If the cockpit is done in 3D (lets say for VR) then TrackIR would give the same immersion. It would allow you to look out the windows like it does in a flight sim. I just finished adding TrackIR to Everspace using its freelook. It really adds to the game. It doesn't give you any more advantage in what you see but just makes it more natural to look around instead of using mouse/keys to change your viewing direction.
I would like to see native TrackIR support added to DU either with NaturalPoint SDK or the Freetrack SDK (which is probably cheaper way to do it) but if they at least give us the ability to bind the mouse to freelook you can use a work around. Even those that don't have TrackIR (or can't make a cheap DIY version) people can still use the mouse or trackball to look around. Of coarse a 3D cockpit would be preferable but then again it would be necessary for VR support as well.
It is pleasing to see community developers add TrackIR to older games like Descent D2X-XL and Freespace 2 Open. Also some smaller companies like Marauder Interactive's House of the Dying Sun took the time to add support for TrackIR. I understand that it is fairly simple to add TrackIR support but companies seem to want to come up with excuses as to why they don't. If you can support VR then you can support TrackIR. I dare say there are probably many TrackIR users and will probably be more when they realize they can't afford a VR setup.
As someone who uses it I can tell you it is a great immersion experience. One would think it would be awkward to get used to but actually when your profile is tweaked it is very easy to get comfortable with. Let's see how long people can hang a VR headset off their face before their neck muscles start to scream.