What gets me is whether having two of the same engines would actually make a ship faster. Thrusters, sure two would be better than one... But a warp engine?
That's my argument. Although-the way you've phrased it doesn't mesh with what I thought you were asking.
Rather, I would ask this question: Is it possible to generate two warp fields with one ship to any benefit whatsoever?
The answer is a solid no.
I've been thinking about this, and my solution thus far is to remove engine components entirely, and have "smaller" versions of the engines be simulated by adding minor miniaturization amounts to the subsequent engine techs. I think that this should be balanced out by setting a negative miniaturization modifier when each new engine (i.e. impulse, warp, hyperwarp) is unlocked-in addition to their +speed, obviously.
I haven't decided what speed values to give them as of yet, or how long the engine tree necessarily needs to be, though.
In any case, it beats the hell out of making 5 new hulls for every engine type.
I actually agree with this, concerning 'engines' or 'drives' that propel a ship from system to system. That main engine may become more powerful, or more compact... But in essence, all of the components whether they be single or multiples really all adds up to being one big engine, or one big drive system. I like the idea of a % of the hull being engine or drive. I also like the idea that as tech increases, the speed increases and size of the components gets smaller. You would have to have definitive ship classes that could travel between systems, and those which would have to be transported there on cargo ships. (Now your talking actual logistics too... )
I also believe there needs to be a Thruster tech line, and they need to operate seperately. They need to be tied to a finite fuel source and they should be able to be applied to a hull in multiples affecting the speed.
As for techs, the games levels for engines or drives is fine. From an Ion engine @ speed +1, size 35% of hull to first level Warp @ speed +5, size 25% of hull... Maybe each level loses a % and adds a speed??? I'm sure it would be self evident where the values would fall once you matrixed it out.
@tetlytea: Yes, space is big. And we want control of it... All of it. Oh, and did we mention, it's OURS. That includes the space around our planets, the space between our planets and any space in between. We don't want you in it. You do not have the right to build starbases here, nor to patrol here. In fact, you're not welcome here at all. Every race has the right to set up a defensive perimeter, a zone of whatever you want to call it, influence or whatever. Between your influence and mine, there needs to be a place that is open. A buffer zone... A nuetral zone, where we can keep an eye on each other, a border.
It's not copying anything. It's the way it is. It's how that system is executed that sets it apart, that decides whether it copies anything or not.
It's very true you could not patrol this vastness of space. I am sure stealth technologies would exist that would allow incursions or raids into enemy space that were 'undetectable'... At least until it was too late. But we have all kinds of neat sensor technologies and space stations and fleets and drones to keep us apprised of your actions. We are diligent in our patrols, and I think we do a pretty good job of it. Do you think you can sneak in undetected and wipe out a colony without us finding out? Go ahead and try, it's what they invented war for.
What it all comes down to is simple... You're just mad because we won't let you travel in our space. 
T