Upon testing the Sidar, and Extramodmod's version of Sever Soul, I think it is a decent replacement for any Dimensional1 functionality that might have been gained. Therefore having Dim1 added to Ghosts is unnecessary, and perhaps even redundant.
Therefore at this point I would propose only a minor change.
Currently ghosts are 5/3 +1 poison, stealth, hidden, marksman, and -50% city strength.
I would suggest adding +10% withdrawal (up to +25% but I think +10% is fine, especially if we consider the second change) ... and +50% city defense. I don't mean -50% city attack and neutral city defense, but an actual +50% city defense.
Normally an Assassin attacks into a city at '3', and defends a city at '2' strength. Or in other words, assassins without levels aren't good anywhere near a city, unless the defenders have had some massive collateral, and they are never decent defending a city .... almost ever. Perhaps Aeron's Chosen with Combat 5, 5/3 +1 poison +2 unholy has a decent city defense potential at 6 str +50%, or at 9 str .... but most assassins defend a city at 2 str not 9 str. And a non-Aeron combat 5 assassin will defend a city at 6 str. Compare that to a normal combat 5 assassin's strength attacking 'into' a city at 9 str.
For the ghost to have a +50% city defense boost, this 3/2, 9/6 business would flip somewhat ...
a ghost would have 4/6(lv1) and 9/10(lv6)
Now, if instead we simply remove the -50% city defense, we get 3/4(lv1) and 9/8(lv6). Again, these numbers are Attacking into a City/ Defending a City. Of course these numbers can be altered with a city having high cultural defenses, palisades and walls, archery ranges .... in which case the penalty is greatly reduced. But for such an expensive unit, whose primary capabilities, granted, are of an offensive nature, and for a civilization whose lore ....
Well, simply removing the city defense penalty might well be enough. I will offer this though ... the Sidar cities are shrouded in mist (typically) far more deeply than its countryside ... with people traveling in and out of sight, and within a city is exactly where this thematic 'invisibility' becomes useless ... therefore, for the Sidar's most iconic invisible unit, I feel as though a city defense boost would allow it to embrace the 'national defense' theme of the Sidar while not sacrificing its offensive capabilities, or making the unit any stronger for an offensive campaign. (that's what the sever soul and withdrawal are for ... and with hawks still able to see ghosts, its a fair shot imho ^_^ ... the mobility isn't quite as good as commando, typically, and with the correct strat defenses *can* be prepared.)
Now, to reiterate, I'm retracting my dimensional1 request ... (for the most part).
Here are several different versions
Mk.Ultra --> +10% withdrawal, +50% city defense, Dimensional 1
Hidden Ninja --> +25% withdrawal, +50% city defense
Moderate --> +10% withdrawal, +50% city defense
Conservative --> +10% withdrawal, neutral city defense
Now I know you aren't fond of me leaving this at a list, so I would naturally propose the Moderate option, with a moderate yet effective +10% withdrawal from the base, as well as a hefty +50% city defense (which is a massive increase from base -50%). At 3 +1 poison defense str however, this would only make a ghost *still* subpar to a city garrison champion under similar circumstances .... but it *would* make city defense a real possibility for a player that chances at making more assassins than say, rangers or champions. A strategy that would normally spell doom, and therefore discourage the widespread use of a UU that is, imho, less powerful than the easily spammable firebow. Or in other words, assassins are typically so poor at city defense that even in a game that typically encourages attacking 'out' of a city, the weakness of this element is enough to discourage the widespread use of assassins for the sagacious player. I do think that the larger benefactor here would be the Sidar AI, that it may more freely be coded to make use of its precious UU, which otherwise would spell its doom, and also that the AI typically defend its cities with a rag tag of all sorts of units anyways, that any city defense with a ghost would help the Sidar AI more than the Sidar human.
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Added Martyr Blades (mercurian) and Executioner (Infernal) as Assassin UUs in the issue. Only change is switching the 'poison' damage to holy or unholy respectively.