One problem I'm seeing with BM is the AI building Fighter Bombers with no weapons - just lots of armour. Since they then run away from any combat, chasing them down becomes a bit of a hassle.
In terms of changes - how about a rethink on engines? There seems little point in having separate tech fields for the different types now since the main difference is movement point generation, so why not either (i) combine the tech areas (Ion, Contra-Terrene, Jacketed-Photon, etc) into a general Propulsion technology or (ii) vary the movement point generation so that later technologies improve at a faster rate?
With (ii) you could, for example, set the formulae so that new techs start off with fewer points but improve faster, making them more suitable for long term investment, e.g.
Code:
Engine type______Current formula_______________Suggested replacement
Ion..............100 + (([%Level%] - 1) * 5)...100 + (([%Level%] - 1) * 5)
Contra-Terrene...115 + (([%Level%] - 1) * 5)...100 + (([%Level%] - 1) * 7)
Jacketed-Photon..130 + (([%Level%] - 1) * 5)...100 + (([%Level%] - 1) * 10)
Quantum..........145 + (([%Level%] - 1) * 5)...100 + (([%Level%] - 1) * 15)
With this, Contra-Terrene engines would need to be developed to level 3 before outclassing existing (prerequisite level 3) Ion engines, making level 4 or 5 Ion research a practical option for empires needing faster ships urgently.
Similarly Jacketed-Photon would need level 3 and Quantum level 2 to equal or outclass their prerequisites. It may be worth adjusting the prerequisite levels to increase the lead-in time for new propulsion types, but the overall effect should be to provide distinct short-term/long-term research decisions.