There is always the need for more interesting props to make game scenarios more varied and interesting.
For instance instead of yet another attack on some race's usual freighter why not a mining station, trading post, trawler, ore carrier, barge, transport, ferry or tanker??
I created a prison transport for a particular Orion Pirate jail break LAN scenario two years ago. Players had to secure the transport, along with the key prisoner to be rescued, and escape before the authorities prevented it. Some had to run interference. It took several attempts and much team discussion to eventually win and escape with the prison transport over the map edge. Six players, one cloaked LR+ each, AI authorities triggered on first hostilities against prison transport or escorts.... a lot of fun.
All of these have been modelled by someone or other and exist in all versions of SFC for downloading somewhere.
Most of my modelling comes from having to provide strategic objectives and facilities for LAN campaigns, including logistics support, smaller patrol, escort and perimeter action type vessels plus attempting to add in all the various things from SFB that were missing in SFC 1 (and other versions) such as various space mines.
I've always been interested in the "other" ships in any of the Star Trek timelines. In TOS, DS9, TNG and ENT many are just mentioned in canon either appearing as on screen communications, sound only communications or as a mention of "receiving a message from...." types of canon.
In one TOS episode the names and numbers of starships available in a sector only appear on a noticeboard on an office wall.
Still lots of stuff to be modelled....