I think it's a brilliant idea... the only problem is that it might not actually work. If it does, we're rolling... I'll just build a crap-load of them (having no engines, these "ships" are quite quick and cheap to build) and park a bunch in orbit around each Gas Giant that has a decent concentration of Sorium. Send a Tanker once a year or so, to suck out all the refined fuel, and leave them to it.
... and it gets even better!If this works, why not Terraforming Space Stations? Build several "ships" with no engines, but with as many Terraforming modules as I can cram in... and use Tugs to drag them over to a nearly-habitable planet such as Mars. Park them in orbit and let them go to work. The really clever part is that Planetary Terraforming Installations... the ones that you build on the surface of a planet... require 250,000 colonists to run each installation. But the ship modules don't. That saves me 250,000 labor for each module, and I might be able to cram several modules into each Orbital Station. Those couple-of-million colonists that I save by using Space Stations instead of Planetary Terraforming Installations can be used to run mines or factories instead.
http://aurorawiki.pentarch.org/index.php?title=Terraformers_(Shadow)
Genesis class Terraformer 1,506,050 tons 10250 Crew 27005 BP TCS 30121 TH 0 EM 0
1 km/s Armour 1-1170 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 1 PPV 0
Maint Capacity 11 MSP Max Repair 500 MSP
Habitation Capacity 50,000
Terraformer: 50 module(s) producing 0.175 atm per annum
This design is classed as a Commercial Vessel for maintenance purposes
This design is classed as an Orbital Habitat for construction purposes
That design from the wiki is a bit more advanced then your current tech, but shows that the idea is quite valid.