[Rigelian]

Well, with all of the scientists in your empire working on the problem, and a two or three month travel time, that is not entirely unreasonable.

Hmm - diminishing returns apply to research too you know .. so putting all the scientists on it may not gain you much. But in 'game' terms I believe that even a six-month travel time should not result in you arriving on the battlefield with effectively useless weaponry.

I think that the ratios of technological advancement to ship construction times to 'time to battle' are very difficult ones to get right, and historical precedents are not usually directly translated into a good game balance. I have yet to see a (sci-fi at least) game that rewards 'dispersion' of fleets over a territory over making 'one big nasty stack'. Yet that would result in lots more 'cruiser actions' and a better game overall.

I am currently running my first game in a long time, and using High tech cost. So far it looks promising in holding back the arms race. My overall approach is that a ship design that I built a year ago might get beaten by half the number of my latest model - but should not be useless against it.

Rushing down tech areas to get the final uberweapon of that Category is one of the things I don't like and is on my list of things to mod out.

I think High tech cost does the trick nicely on that one already. It costs MILLIONS to get to the end of Energy Stream for example. Same with Shields 10.

Higher research costs is only part of the equation. Having much longer tech trees, with diminishing returns is another. Adding Grid techs instead of linear techs will also help.
(EG: Multi tech areas: DUC damage, DUC accuracy, DUC durability, DUC mass production)

I don't think I would go down to that level of granularity. What I would do is make the tech tree a directed graph instead of a tree; like the Civilisation series games for example. To give a couple of examples:
Cloaking might need Astrophysics 2 as well as Physics 3.
Troops above level 1 might need Psychology (or Computers, alternate tracks).
ECM level needs matching level of Physics, as well as the prerequisite Mil. Sci.