A few years ago, a workmate and I joked about having a 'model-off'. We both bought the same 1:48 Tamiya Spitfire mk1 kit, and got cracking.
First thing I did was some web research: I wanted to kick his butt with a super-detailed kit, so I needed to see what inaccuracies would foul this model if built it straight from the box.
The cockpit, the canopy, the prop, the wing-weapons, the wheels, the rudder and all control surfaces were details that could be improved. Resin, etched-brass and vacu-formed plastics from various aftermarket sources soon quadrupled the cost of the build, but would eventually make it look amazing.
A Haynes manual of the Spitfire also found its way onto the hobby shelf: obsessive reading and trawling the web for close up photos, and triple-checking the correctness of the details was how I spent many evenings.
I started the project, and got a decent way into it, but then had to put it on hold for a while, and then shelved it for much later, and then moved house, and now I don't remember what any of the aftermarket bits are for.
When I do start it again, it will be awesome, but I'll have to obsess about it again, and to the same level as before.
My workmate, sadly, got divorced, and I don't think he finished his model, either. If he did, it was probably only an average attempt ;-)
I've had a similar story with a Halcyon Aliens Dropship (detailed, kitbashed, but not finished) and a paintjob on a Suzuki Whizkid - finished for a commission. Hours of checking details and finding methods of getting them scaled down - over the last 10 years I've learned how to make my own decals, how to use an airbrush, how to cast resin, make moulds, and how to make my own etched brass parts.
Bottom line? These days, for the majority of my 40k builds, I'll read backstory for continuity, and check the codex and online sources for reference pics, but rarely will I go totally nuts for super-details.
Which is why my Space Wolves terminators have resin torsos, my Tau have fancier decals, and my tanks will have brass and resin upgrades.
And they're all still WIP.
Here are some other union posts you should read:
Sven Harjacek's Scale models
Fill 'n' Sand