The spacing between systems is not the issue I thought it would be, however the planet spawns seem to be back to "almost everything is dead within 50 tiles of your home system" even on Abundant settings which I find to be not fun. I took a look at the mapsetupdefs file, and it does look different than I remember, makes me wonder how I am supposed to tweak it now.

So many modders....so little answers.

Yes, I also will love to know: starting a game with  a class 12 planet in retribution, well, Sucks!

I almost miss the original GC3 where you could edit everything with ease!

Make a copy of PlanetDefs.xml.   Check.
Simply edit the value of the Sol system (Earth from 12 to 25)  Check.
Make sure to uncheck and re-check "enable mod" every times and reboot game.  Check.

For each edition/combination: game was restarted with new game both with the default Terran and with a game created custom race who use the Sol System.

1) Copy PlanetDefs.xml to:
Documents\My Games\GC3Crusade\Mods\Example Mod\Game folder. 
Check. =Not working.

2) Copy PlanetDef.xml as stand alone file in
Documents\My Games\GC3Crusade\Mods\Example Mod
Check. = Not working.

3) Create Commonsensmod folder in
Documents\My Games\GC3Crusade\Mods.       (with same structure as in \Example mod...with all 5 folders)
Check. =Not working.

4) Create new PlanetDef.xml with a new star system, edited also StarsystemDefs with the new star system  etc etc
redo all 3 combinations
Check = not working  and cannot even found the Star system in game selection.

5) Re-read again the Moddingreadme file stating :
""When creating new mods follow the file structure demonstrated
in the ExampleMod directory. The game will read the directories here
in the same way it reads them in the install directory. Each
mod must have at least:
ParticleScriptDefs
Text        
Core        
Game
These directories correspond with the directories found in the install path
GalCiv3\Game\Data\. Each type of xml file must appear in its corresponding
mod path in order to function correctly."

Check. Delete everything and redo it all over taking my time = not working.

6) Do a voodoo dance dressed as a chicken under the moon while sacrificing a twinky to the god Linus Torvalds while swearing that my next gaming computer will not use Windows.
Check = not working.

7) Do it all directly to the games files in
Program Files\steam\steamapps\common\galactic civilization III\data\game
Check =  not working and its not even bothering the game at all. (?!?!?!?!)

8) Download Horemvore's modpack .rar file (to check how he did it and structure) (done 3 times)
Check = not working: cannot open file  as its not even recognized as a .rar file  and thus cannot even check it. 

9) Download and open other mods (grm).
Check. = found nothing special in their files or structure (didn't bothered to check if they work though in game)

9) Refrain to smash computer and/or lobotomize myself
Check = Barely.

Am sure the solution will be simple and may make me feel stupid for weeks, but it evades me ( and 2549 others it seams) completely.

Yes, I've tried both approach ( Append and total conversion) with all the combination possible.

Thanks Horemvore for both quick and apt reply.

Did used the direct link and the files where unzipping perfectly. Booted the game and YES! the UCP mod where in there. Selected one of the 2 Sol system: here we go! works!

For my personal education (heck! purely by pride) I took a looksy at your files and cannot figure out (yet) how they differ from the ones I created...ill go over it piece by piece over the week-end.
If you do not mind and for my personal use only, may I edit your files so that the game reflect what I want?

So great! modding this game to make it interesting again is solved.

Now i face another problem: since I have no more reasons to smash my computer to oblivion, have to find a way to justify to my wife a reason to spend couple of thousand$ on building  another one....ill think of something.

Again, thanks man!