Failure rates modification
I think it would be realistic, if ship components of older tech than currently posessed, add less failure rate when installed on a ship.
This would reflect the ship designer's, and the crew's familiarity with components which have been known and tested for a longer time.
For example, say you have researched ECM 6.
Before you researched ECM 6, your ECM 5 components added x% to the ship's failure rate.
I suggest reducing the failure rate by 20% per tech level researched, that is more advanced than the one installed, with a minimum of 20% of the original value.
So, installing ECM 5 in this situation would add 0.8x% to the ship's failure rate
If the standard failure rate of ECM 3 would be y, in this example, installing ECM 3 would add only 0.4y% to the failure rate.
ECM 2 and ECM 1 would both add 20% of their standard value to the ship's failure rate, as the minimum is 20%
For racial techs, I'm not sure how determining a component's failure rate works, but it would make sense to use the average reduction percentage to determine the component's final failure reduction.
Example: You have Ion engine technology researched, thermal reduction 35%, and fuel efficiency 70%
Now, you create an engine with Ion technology, thermal reduction 50% and fuel efficieny 70%.
These technologies have respective failure reduction rates of 0%, 20% and 0%. This averages to 20/3 = 6,67%.
However, like I said, I'm not sure how calculations work as they are now. If in the example above, thermal reduction does not change the component's failure rate, it's percentage modifier will not be included in determining the component's final failure reduction. In other words: only technologies in a component that affect it's failure rate in the first place, are used in determining the final failure rate reduction.
This would also make the construction of *huge* deathstar ships more feasible. Just use older techs for the components that aren't critical to the ship's doctrine, to help keep it's failure rates from rising sky-high.