[Arkcon]

Of course, a bunch of frigates with boarding parties will overcome a dreadnought's defence, and trigger the auto destruct sequence. A swarm of these sacrafice frigates will inflict some serious carnage on the opposing fleet. IIRC, the latest patch will have boarding ships suicidally board ships with self destruct devices.

[EDIT]

Dang, I'm slow today. But my comment still stands -- research a few levels of boarding parties, put them on your smallest ship, maybe with fighters armed with small shield depleters (shields will start appearing soon), can be a fair tradeoff against big expensive ships.