Latest Version is 2.5.3.1.
Aloofi, you might want to consider fighters with cluster bombs for planetary attacks. Of course, you might also want to be careful not to wipe out the colony entirely. ;-)
Homeworlds are supposed to be very difficult to capture, naturally. This is both a realism issue, and a game balance issue, since capturing an intact or even semi-intact homeworld can give the captor a critical advantage over all empires with only one homeworld. However, it's quite possible (though certainly not easy without a very strong and appropriate force) to take one from the AI, or an unprepared player (humans are tempted to deploy outward rather than stock up on home defense that might never be tested).
I may add some more repair and construction levels and variations in a future Version, if/when I get to it. However, I tend to think that bases with construction and repair components provide plenty of ability to do this, and I like that they have a maintenance cost, a separate presence/target in combat, don't compete for facility slots, and don't remove the interesting obstacle and balance factor of having a signifigant time requirement to build major units and facilities. If it's possible to get a really big planetary construction rate, then it sort of erodes the balance and interesting limit on how long it takes to build the more expensive items. I like Dogscoff's suggestion of adding levels with diminishing returns. I had been thinking of adding more wimpy starting levels and a slower progression to the current levels, too, so construction becomes a more interesting choice for major research (or not).
Temporal tech has a major advantage there, but are you saying that their advantages are better than other racial techs', or better than 1500 points spent on other advantages? So far, I don't really see any of the racial techs as being clearly more powerful than the others. JLS was helping me evaluate that a bit, though I think one or both of us sort of forgot about doing that, or maybe an email didn't get through.
I'd be interested to hear from players who have tried a Temporal empire in Proportions - what were your game settings, how long did it take you to develop temporal spaceyards, and how much of an advantage did it seem to be once you got them?
PTF, Arcology is not on the urban upgrade path for two reasons. Firstly, the upgrade benefit of going from Minor City to Arcology seemed too much to me at 50% upgrade cost. Secondly, an Arcology is really not just a larger Megalopolis. You can't pile a bunch of megabuildings on top of a Megalopolis and get and Arcology (instead, you'd get two Megalopoli). An Arcology is something quite different, and has to be built from the ground up (also, it has cool new pics courtesy of Bill Elliott (mlmbd)

).
PvK