I would personally advise against purchasing another pledge if you are so well perched on the fence as you currently are. All the ships will be obtainable in the game come release, and you can earn them there. If you are doing this so that you can contribute more, buy a shirt or two, a mousepad (which from experience I can state is a good damn choice) or a Gretcat (Greycat is love, Greycat is life).
If you do want to expand your hanger desperately though, just wait until that ship comes out that leaves that nerdtastic smile on your face that makes you look like a retard and always takes too long to leave. Pure desire should be the only contributing factor in these pledges, especially since the full capability of them will not be seen by the community until we can actually customise them to our own preferences.