Since i dont have a computer with the game, or with my modding tools, this is a brief discription of an idea that someone else may want to give a try until i can get back together with my stuff. 

The idea is to take the levelable weapons which the turrets have and use that as a base for capitals and frigates and cruisers. This may be fairly easy to do (i am hoping) 

The second part of levelable engines is something im not sure is doable without the Devs, or the higher experienced modders, but basically is along the same lines as the weapons levels. Producing perhaps sub-light engines for all craft including capitals when first built. Level two or three introducing planet to planet travel by phase lane at about half their normal speed, and then at level 4 or 5 having the engines with a higher efficiency and boost to about 125 percent of their normal speed. So a Capital that has a normal speed of 100 looks like this"

level one   =  sub-light base speed - 25, no phase lane jump available.

level two    =  phase base speed - 50, phase lane jumps available.

level three =  phase two speed - 125, phase lane jumps available.

In the fuel test mod that i was putting together with the idea that Lord Tariq so helpfully thought of, helped alot to get the basic idea up and running. Basically a zero speed as base and then having the speed boost ability bring them up to normal speed.

With a modified version of this perhaps we can get engine upgrades for ships along the same lines as the weapon upgrades. Maybe.

Just some ideas if someone wants to try and let me know if this works or not.

Thanks and take care,

-Teal