[psimancer]

closer to the original subject
of mods vs shipsets

in spaceempires mods are actually more used as a way of changing the physics of the universe and adding components
specifically space empires basic uses non newtonian propulsion wheras most mods attempt to add some measure of newtonian physics to spaceship movement
and almost all mods add componernts for ship design like new and different weapons different armors different engines
some are designed to allow simulation of specific mass media environments
an example the starwars rebellion mod is designed to add components ship hulls movement and weapons that simulate the star wars universe

wheras shipsets/races are a set of pictures and sometimes also behavior control files (a.i and minister)to add flavor to the playing experience as such the race/shipsets have almost no impact on game mechanics (exceptpossibly in the mind of the player)

mods range from as little impact as fqm deluxe (allows the generation of larger more populous maps with more realistic terrain features)
to star wars rebellion
to a full change like space food empires or backyard wars (the toys will own your yard !!!!!)

so in actuallity you might try a few mods
the suggested basic mods are fqm deluxe and the image mod (adds additional images for use by other mods )
many people who play single player believe the game's a.i. to be easy to beat so one masterful designer created the TDM mod to add further smarts to the ai and make single player games more challenging

as such you might discover some of these more basic mods could add a bit more challenge to your single player games