Pawel is absolutely correct in his recommendations. I have worked in the 3D printing/rapid prototyping industry since the early nineties at the service bureau andOEM equipment manufacture levels as a design/mechanical engineer and manager.
I have the same experience and time with CAD, CAM/CNC and silcone mold making. I could write a book on the subject, but from a scale modelers point of view and have access to all of these toys, here is my take on the subject and recent experience.
A year ago, my oldest son (37 years old) bought a Makerbot 2X to build 1/10th scale RC crawler parts. In the last year he has put 2400 hours on the machine. he only builds parts in ABS, as the PLA, PET and Nylon materials aren't really meant to be sanded,bonded or painted. He picked up Solidworks pretty fast and I gave him my Next Engine 3D scanner a couple months to round out his shop.
Since buying the machine he has upgraded the system with aftermarket CNC'd aluminum parts that support the build platform; replaced the OEM heated build platform with a third party unit; reflashed the CPROM with third party software; and he uses a third party software program for all of his part slicing and build setup. So today he is building some pretty high resolution parts for 1/10th scale use.
So from my perspective using 3D printing systems for model parts for myself...
Detailed Parts
The best detailed parts come from Objet based printers. I have seen and handled 1/1250 scale ship models that had details that would blow you away. But Objet systems are pro level and very expensive. Shapeways or a service bureau is the way to go for highly detailed parts directly out off the printer. Some of the SLA base systems can get close, but I would only use an Objet printer in these cases.
"The Real World" of FDM/FFF 3D Printing
I use only ABS for building parts. And ALL the parts, except for build fixtures and tools I have designed require finishing. My preferred modeling method is to use #D printing as a starting point or base for either a epoxy molded or vac formed final part.
I use the system for what I call near-net parts...I get to 80-90% of the shape I want on the printer and use a hybrid scratch building approach to get to the final part. Here are the projects that I have used the FDM/ABS printer for.
FYI, all ABS parts have to be scaled up in CAD by about 3% to allow for "skrinkage" as the plastic cools down...this is the same issue with injection molded parts as every plastic shrinks as it cools down to some degree.
1/35 Armor - 90% near-net models - tank and truck main bodies, turrets, and masters for epoxy molded cupolas and fuel containers/accesories. WW2 German armor is easy, a cast hull Sherman takes time.
1/72 Aircraft - 90% near net with some finishing, primarily filling and thinning - fuselage, wings, rudders,elevators, masters for vac-forming canopies, some ordnance. I have made masters for radomes (AD5N, P2V, EP-3,etc).
1/48th Aircraft - Same as above but add in engine housings masters (B-17, B-24) masters for more ordnance molds as well as larger masters for vac-formed parts. I have made a few interior parts like cockpit tubs for modern jets, and a few "masters" to scratch build ejection seats around.
1/25th Cars - fender flares, seats (like Recaros), interior panels masters, engine blocks, and custom fixtures for scratch built, tube chassis.
I have a lot of years doing this so I can design a part that I want in CAD understand the best process I need to use to get to the final part. Pawel is right on point...and my recommendation is to use 3D printing as a add on to your scratch building needs...not a replacement as the FDM/FFF technology isn't ready out of the box for for the likes of us and our expectations as scale modelers.
I would recommend looking at OnShape as a CAD tool, if you dont have any previous experience in or with CAD.
Cheers