yes- it would add great realism to the sound and overall experiance. maybe even use EAX. Its a type of sound that most modern sound cards utilize and it works out what sort of sound you need depending on where you are.
Ie: sailing through a tunnel with the tug: the engine would be vibrated and reverbed in just the right amount to give realism and depth to it. Many games already incorporate this. I.e, Need for speed, Colin mcrae rally 04...I know theyr'e both car games, but surely ss could use it?
But, only a suggestion- otherwise, the xtra SFX idea would be a very wise addition, especialy in the smaller ships.