Gord yes! I have long advocated that civilians should build only one type of ship -- for many reasons, including that my luzury cruise passengers would not be susidizing more infernal CMCs.
While I don't share Father Tim's seething hatred for the mere idea of private shipping 
, I do agree that having the various civilian companies specialize would be neat. Having most lines operate only one category of vessel, with a chance of expanding to others as they get more wealthy would be neat.
It would hardly change anything. Aurora assumes the two things are equal, and since it is already selecting 'the highest of {group}' adding more elements to the group under consideration would only have an effect if your empire, for example, increased wavelength before increasing size.
A better question is why does ground force weapon strength completey ignore gauss cannon tech? My empire is in the strange position of having to research a completely foreign weapon to make any progress.
Both of these could be addressed together - make racial ground weapon strength based on the average of your research into one of the weapon categories that are flagged as ground affecting. I'd vote for railguns, gauss, laser and possibly plasma, personally - the first three have three techs that make sense for impacting ground combat, and plasma has two, making it a little cheaper to research up ground weapons. I wouldn't want to have to select which weapon type a unit is using, just use whatever option produces the highest number (though throwing an automatic entry in the stat block of an element when it was built showing what category of weapons it's using could be neat for fluff reasons. )
While this means you won't be as penalized by not researching a specific sub-field, races who invest in all the techs in a type will be better with them than ones who neglect one or more techs, which brings some nice verisimilitude.
Part of the problem that people seem to be having is that the civilian fleets expand too quickly. Demand limiting would nip that in the bud. I haven't seen mention of it here, so I'm going to repeat a suggestion from the old VB suggestions thread.
Suggestion:
Track civilian ships' idle time to limit growth.
Suggested method:
For every civilian shipping line keep a counter for each category of ship they operate (freight, colony, liner).
Every time a ship can't find work, increment the relevant counter.
Every time a civilian line considers building ships:
-check the counters to determine eligibility.
-only build categories with counters less than (idle ship limit*production cycles since last check).
-reset counters.
This will limit each line to (idle ship limit) surplus ships per category.
