Just some comments. I appreciate that you're trying to be creative and brainstorm, and these may sound harsh, but we get the best mod by thinking hard about proposals. Testing to destruction - a very Dune concept.
As proposed, Spice Refinery Improvement.
We already have a Refinery as a building. My feeling was that in-desert refining/handlnig was already represented by the harvester improvement.
However, we could have a refinery building in the city that gave extra bonuses for harvester improvements in the BFC.
Planetfall had a building like that, that gave a bonus (free specialist?) for each robotic mine in its BFC.
provides +1 gold per adjacent spice tile
This seems weaker than a cottage - you will hardly ever have a tile adjacent to more than 2 spice tiles.
Also, more things where you have to contantly have to run around rebuilding improvements because of spice blows/evaporation? Doesn't seem that much fun. Unless you're intending for this to be built on deserts?
Also seems like a lot of work to code (sdk mod required); there aren't any buildings now whose yield depnds on the presence of things in adjacent tiles.
Do you remeber those consdtruction units from Westwood series, which can build base? For me, in late dune such mobile construction platforms make alot of sense. So, late in game MCV unit
An MCV seems very un-Duneish to me. That kind of thing was built for the computer games for standard C&C gameplay mechanics, but nothing like that appears at all in the books. Maniac tried something like this in Planetfall with a supply crawler building robotic mines, but then later removed it I think.
b. Improvements, which are aviable late-mid/late in game, are iusing Demagog Mechanics from FFH. If being worked, improvement grow, and when it grow enough of turns, it spawn some kind of unit, and improvement resets.
The AI allocates tile work (and improvement construction) based only on resource yields. So, if this improvement gives as good yields as other resources, then it will be too powerful, because it also gives free units. If it doesn't, then it will never be built or worked.
Also, why should terrain improvements be given workers; some kind of militia being levied?
a2. Trading post. +2 commerce, +1 culture. When grown , spawns Trader (simple) which just can go and generate some cash with your OB neighbour. (neet to check and ballance yield)
Trading posts in the suburbs of your own city? Feels weird.
Also, improvements can't generate culture.
a3. Training Camp . Spawns current era melee unit. (Intersing use for warmongers and some bad tile cities.) (make alot of sence from canon Dune too),
Units should be trained in cities, not by improvements. Thats how the civ engine works; the AI knows how to build units in cities, not by working tiles.
If it has a low yile yield, the AI will never build it, if it has a high tile yield, then it is too strong.
improved rate of unit production in comparison to city that have not +% military uniot production bonus.
I don't understand this.
Planet Study Center. +1 hammer +1 commerce, spawns Probes.
What is a probe?
None of the factions in Dune other than the Fremen and maybe Atreides have any interest in studying Dune either. Elrood sends Kynes to Arrakis and then just ignores him, and Shaddam ignores his son.