[Suicide Junkie]

I like the idea of having the construction costs go up exponentially (size squared?), while firepower goes up linearly, and maintenance costs rise much slower (square root of size, perhaps)

This means you can pump out lots of firepower in a short amount of time by building tiny ships, but the maximum strength of your military will be limited.

In peacetime, you can spend lots of time and initial resources to build large hulls. With the lower maintenance percentages, you can get much more military strength built up before maintenance starts to crunch your economy.

Medium sized ships would be for those unsure about the political climate, with intermediate strength per maintenance dollar, and intermediate build times.

I think this would make for a very interesting game, with a variety of ship sizes being fielded.