Refinements should upgrade everything related to that particular technology so we don't have Plasma Cannon v1, v2 and v3. Instead "Plasma Refinemant" would increase the damage and efficiency of all Plasma Weapons, as well as improving anything else realated to Plasma.
We have 3 kinds of techs:
Theories, Applications, and Refinements
Theories don't produce tangible results, but open up new levels of Applications
Refinements are a dead-end tech-tree branch that provides quicker results.
For instance if a player has just discovered the plasma weapons application, he can take research in two directions:
the plasma weapon for relatively quick gains in weapon power
2) start researching the next kind of weapon, which will take a lot longer, but be more powerful that the most refined plasma weapon.
Though the engine could support it, I really don't see why we should make techs that improve multiple very different categories. Generally choosing which tech to research should be a strategic choice. If the techs improves lots of stuff at once there aren't going to be very many distinctive choices. It also makes individual techs more vague and nebulous if they do several disjointed things at once.