EDIT: Disregard this entire post. It doesn't work. There's a better suggested model a few Posts up 
END EDIT
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Original post begins...
OK, I think the current plague model (level 1, 2, 3... plagues countered by level 1, 2, 3 medical abilities) is far too simple. Here's what I'd like to see...
First up, plague damage to population should be in proportion to the population on a planet, not a set figure which applies to any planet.
Secondly, plagues should be able to spread from planet to planet, including to neighbouring allied planets. Planets with space ports should be particularly at risk.
Right, now onto the complex bit:
A plague's severity should be measured as a percentage. 0% means no plague. A small number, for example a 3% severity plague, would be easy to cure, and would cause only a little anger on a planet. It would kill some, but not many of the population, and could probably even be an acceptable long-term status for a planet.
On the other hand, a 90% plague would be catastrophic, and would bring production to a complete halt, threatening to wipe the planet out in a few turns.
The first cool thing about this suggested system is that the plague severity value could change from turn to turn. A planet with a 30% plague might go up to 40% if a combat occurred on the planet, or if another plague bomb was dropped. All sorts of other factors could be worked out to modify the plague severity from turn to turn. Random modifiers (positive and negative) from turn to turn would be a good thing.
Curing a plague would require a ship with a "cure level" higher than the severity of plague. For example, a med bay II might have a cure level of 30, and so be able to completely cure plagues of 30% and below. Simple so far, eh?
Cool thing #2: A ship with cure level 30 can't cure a plague with a severity greater than 30%, but it can "reduce the symptoms". It reduces the plague severity by either its cure level (in this case 30 points), or to a severity slightly above it's own cure level (say, cure level + 10), whichever is the higher.
For example, ship cure level is 30, plague severity is 55%. The ship can't cure the plague, but it can reduce the severity. Reducing it by 30 would bring it down to 25%, which would make it curable. This would be pointless in game terms, so instead it reduces it to 30+10=40. The plague is made less severe, but still can't be cured by a cure level 30 med bay. Geddit?
In the event that two or more medical ships are in attendance, all calculations are based on the highest-rated ship, with a +10% of level modifer for each additional med ship in the sector. Confused? Example:
Say you had a cure level 70 ship, a level 60 and a level 50. The plague is at 84%. On the first turn the game takes the highest cure value (70) and modifies it by 10% of each additional cure value. (10%of 60 + 10%of 50=11 )That makes a cure level of 70+11=81, which can't cure the 84% plague outright. However, like in the first example, it reduces the plague severity from 84% to 70+10=80% (notice that the unmodified cure level is used at for this Last calculation. There's a reason for this.)
For the next turn (we'll ignore any factors which may have made the plague worse), we see that combined "cure power" of the 3 ships (70+5+6) is enough to cure the plague, which is now 80% severity.
This means that lots and lots of med ships can "gang up" on a plague to cure it. They should therefore be pretty expensive. There is a potential exploit there using the "+10 if can't cure" rule, but external severity-modifying factors will go some way to negating this.
For further complication
a med bay's cure level is also variable over time. The base level of 30 for a med bay II could be augmented each time it successfully cures a plague (experience). Finally, medical facilities on-planet could provide a system-wide "cure boost", which alters the cure level again. These same facilities could reduce the spread of disease from planet to planet.
Finally, curing a plague outright would be a slow process. Assuming the ship or ships have a higher cure level than the plague severity, it might take several turns to reduce the severity all the way down to 0%, depending on the comparative values of the plague and cure. The same would apply when a ship reduces the severity of a plague it can't cure. This would give the plague a chance to "flare up" again if some external event prompted it.
That's about it. I know it looks horribly complicated from my explanation, but it's actually reasonable simple. Ish. From the player's point of view it would be clear what level of medical technology is required to cure a plague, but at the same time the plague would appear to have the unpredictability of an organic system. It would certainly make a lot more sense and provide a lot more challenge than the current system, anyway.
[ August 29, 2002, 16:30: Message edited by: dogscoff ]