Just some thoughts on other neglected tech areas...
Biology - Nobody researches this one, maybe they would if it gave some facilities that increased population growth rate and happiness (like the Organic races have), or smaller and cheaper life support components for ships?
Planetary Weapons - A lot of the weapons in here are really cool (Planetary Napalm does massive damage, but only to planets, Smartbombs seek out spaceports and resupply depots, Neutron Bombs kill population even quicker than plagues, Radiation Bombs prevent population from growing - why isn't there any "Only Planet Value" damage type???
now THAT would be useful!
) but nobody seems to use them much... wonder what could be done? The tech's pretty cheap already...
Also, there are a bunch of techs that are way too cheap - once you research their often arduous prerequisites (if they have prerequisites), you can blow through each level of the techs in one turn - this goes for things like Point Defense, Advanced Military Science, Warp Weapons, Gravitational Weapons, Phased Energy Weapons, Ship Capture, Explosive Warheads, Smaller Weapons, Tractor/Repulser Weapons, etc. - just doubling the cost of these fields would make the game more interesting, with a more diverse spread of technology (one empire might have PPB II, another might have PPB IV)
Oh, and maybe more levels of progression for the fighter/troop weapons would help - as it is, there's a BIG jump from, say, DUC I to DUC II - the damage and range both double!
Not to mention the fact that you need to research Fighters to get Small DUC's while all other Small weapons come from the Smaller Weapons tech area... did someone change his mind while designing the tech tree?
One more thing with smaller weapons... the Ground Cannon is nice, but does it HAVE to be the uber troop weapon so you don't even think of putting other weapons on your troops? Maybe if it were 4kT instead of 3 then you'd think twice about it... or if it cost a whole lot compared to other troop weapons...