That is definitely true, we are almost all guilty of building non RP kiwiships (or at least those with a license), but that's easy enough to fix. Just do a quick rule change that makes it so kiwiships, just like buildings, must be RP, and if they aren't then they will be demolished.
As far as the lag that the ships generate, what about my suggestion for reducing the lag:
http://kiwike.se/forum/showthread.php?tid=3476
And, boom! Kiwiships now are much more practical!
As far as kiwiship practicality goes, they can be used as anything from mobile pieces of scenery, to transports for massive amounts of goods, more than anyone could hope to carry in their inventory! I believe that kiwiships should definitely be used in the new RP server, as they are one of the coolest and most unique plugins that kiwike has to offer (just after territories of course)!