One thing I did in Astra Imperia was to limit the amount of tonnage a population can support. I'd have to look up the rule to see what the excess incurs, but I believe it was along the lines of 2-3 months of stationing a ship at a population that cannot support it would cost near the purchase price of the ship.
I wasn't going to respond to this thread, but Erik's post kicked me over the edge.
I think that the fundamental problem with PnP SF is that it's trying to be at least 3 different games for three different player archetypes:
1) Naval combat PvP - For this archetype, the Imperial SF part of the game is primarily there to set up "realistic" OOB and start configurations for battles. For this group, the details of planetary population growth, Imperial economics, etc. aren't important - they're just there to provide a backdrop. I view this as the group that's looking for something like Carriers at War.
2) Space 4X PvP - For this group, the opposite is true - colonization, growth of colonies, resource allocation, etc. are the interesting part of the game; the combat rules are there to "keep score" when empires go to war. I view this as the camp that is looking for something like Civilization or Galactic Empires (or MOO or ...).
3) Space 4X role playing - This is the group that likes to write after-action reports. This group
wants lots of random variation in NPR, since that adds interesting flavor to the story of the game. The best I can come up with for this group is D&D.
Note that a lot of this has already been said in this thread and on the board, and that most real-world players will typically be a mix of the archetypes. In addition, there are in-between states such as those who want to game out an entire fleet campaign or war (e.g. 3rd Reich players). My contribution is that #1 and #2 are in direct conflict in terms of level-of-detail and timescales - the tactical game takes place on a scale of days, while the 4X game is on a scale of decades. The problem is that there are a LOT of days in a decade, and a lot of ships in an empire :-) ) - the "detail freak". These are the gamers who like to track and control individual squads in an entire theater (what's the WWII Pacific game of this sort - War in the Pacific?). This is exactly counter to the separation of scales methodology, and winds up with games where the wall-clock-time to play a turn increases exponentially with the size of the empires. In other words, these games grow until the empires reach a certain size, and then they stop. For an example of this, take a look at the size and frequency of turn writeups in Steve's Rigellian Diaries (and this was with computer support). Note that Civilization suffers from this disease too (at least if you micro-manage city production like I do).
In my opinion, Imperial SF didn't go far enough in abstracting away the individual movements of ships and units - it still has the detail-freak disease. The player still gave individual movement orders to individual ships (or TG); as the size of the empire grows, this becomes excessively cumbersome. I think that, in order for the game to meet both sets of needs (4X and tactical) the Imperial game has to be ruthless in cutting out detail - I think this is where Imperial SF falls down.
In order to build a game that doesn't suffer from this, I think one would have to go to a "macro-economic" version of fleet management for the strategic game. Rather than tracking individual ship movements, one would assign ships to fleets which had patrol responsibilities - a fleet would have a certain number of certain classes of ships. Rather than tracking which ships are in maintenance, one would go with the USN's "1/3 deployed, 1/3 training up, 1/3 refitting" ratio to determine how many ships in a particular fleet are available at a particular time. For the single-battle tactical players, one could then use the patrol responsibilities (e.g. 1 CVBG is always in Westpac) to generate random encounters between Navies. For the campaign tactical players, one could randomly assign locations upon a patrol to the various patrol responsibilities. For the 4x players, one could generate "tracer" battles for the various patrol responsibilities that were then multiplied by some factor to determine the entire campaign (or just use straight attrition formulae). For the detail-freak players, they could intersperse full campaigns with 4x segments.
The reason that Erik's mail prompted me to write this is that his statement of "stationing a ship at a population" struck a chord with the thoughts I've been having along these lines. Basically, the 4X game would involve building ships for fleets, stationing them at fleet bases, and assessing the costs of the fleet deployments (in addition to colonization activities, of course). It should be expensive to station a large fleet a long way away from core worlds, unless port facilities were explicitly built up. The player could turn knobs to e.g. "surge" readiness if he thought war was imminent, or set levels of war-like encounters with neighboring empires (e.g. "friendly" vs. "covert harrassment" vs. "open warfare"), but these levels would have costs in the 4X game.
Of course, this brings up the question of how much Crucis wants to change Cosmic away from 3rd Ed. On the plus side, I don't think many people are arguing that the core tactical game is broken (other than maybe the smaller=faster hard-wiring that, in my opinion, is a major contributor to swarm tactics) - it's the Imperial side that has the problems. The question is, how much can this be changed? Also note that none of this is a solution for the exponential growth "rich get richer" issue that's common in 4X games - that would require some sort of change in the economics rules that sets a scale size of empires, so that growth of big empires is (proportionally) slower than growth of small empires.
John