You MUST bear in mind that FS2004 is very different to FSX!!
If you want FSX quality/eye-candy etc, then buy FSX. You cannot expect/demand things of developers.
Have a look at Milton & team's planes. They are stunning in FS2004. There are a lot of other developers, both freeware & payware that have done amazing things with an older simulator.
Also, the FS2004 simmer market has become a lot smaller than FSX, FSX: SE & P3D!
You mentioned scenery! In FS2004, thanks to the late Garry Smith from http://www.ford-tri-motor.net/
We have ramps, circular runways & even sloping runways, as well as a vast collection of scenery, planes & textures, all free for FS2004.
To be very honest, I've been simming since the very early days, & have become bored with the usual point to point flying in (in my humble opinion, after a long time simming) basically the same Airbus's & Boeing's & similar planes. I have a separate install of Golden Wings & also an install of the Ford Project stuff. ALL of which cannot be found in FSX!!!!!!
So, yes, developers ARE actually still supporting FS2004, AND giving us amazing things that FSX cannot!!