Currently, the unit is just kind of lol, since by the time you get there, the game should be about over. So why not have the unit be something different, almost like a walking nuclear weapon. Say, give it 150 Strength, Blitz, Dreadnaught, (or give it a 125 strength ranged attack with Logistics Instead) and have it cost some obscene amount of hammers. So if you do manage to build it, you can have a laugh stomping over the AI as your Spaceship is getting ready to launch.
Yer one of my tribe!
I renamed GDRs to Mecha and gave them 5000 Combat, the ability to carry two Nuclear Missiles, and an experimental promotion that ignores terrain (I dunno how to make them ignore rivers though) and gives them 50 Movement.
I also increased Nuclear Missile's Range (80), decreased its Uranium requirement (1), removed Bomb Shelter's effects on them, and increased their power (so one missile will literally erase a city off the map, then pillage, irradiate, and erase features and units from all its surrounding tiles).
Mecha can only be stopped by 3 XCOM (which I renamed Cyborg and gave 2000 Combat), or 5 Guided Missiles or Stealth Bomber runs (I gave both 1000 RangedCombat), or 2 of WHoward's Mech Infantry (which I renamed Powered Armor, gave 3000 Combat, and removed its uranium requirement), or you can sink them while they cross ocean with Nuclear Submarines (which I gave 1000 RangedCombat).
I modified the World Congress Reformation Mod to lock Mecha, Cyborgs, and Powered Armor behind a project called Spacy Superiority (2nd place allows building them, but 1st lets you enter territory without Open Borders, and 3rd grants 1 Cyborg and 10 units maintenance free). But of course, City State Allies can get them for you through their black market.
I wanted end game wars to be over fast and be completely decisive, with subs and air power determining wars until mecha determine a sole survivor. I do Space Victory first (since otherwise you can't build your starship), then through One More Turn I'll do all other endings and go to last turn so I can see which civilization finally destroys all others. I always play Beyond Earth immediately after Civ 5, and having a worldwide Order or Autocratic civilization (or one lone forgotten tiny Freedom island civilization) sitting in a nuclear wasteland back home allows me to have no moral issues with Supremacy path (otherwise I'd never choose that), and causes BE's story to actually make sense (though I modified that too anyway).
I'll post the relevant pages from my Changes Journal in case you wanna see. I'd post my modified mods too, but I changed way more in them than just GDR stuffs. If yer interested in actually seeing all my other changes though, I'll be happy to post them for you.