That looks like an impressive model there! But unfortunately it’s hard to see much with the small renders. Also, I think you renders are really doing this model an injustice.
All the following will be exactly what I think, without the technicalities of politeness, I just mean it for the best.
pict 1)
Bland background, unrealistic, and honestly, a rather unimpressive angle on the aircraft.
- Landing gear is not touching the surface below it. Bring it down to slightly below the level of the surface, then use a lattice deform to give the tires a bit of ‘squish’.
In general, the materials are really lacking, and it really shows in this render. The tires look like erasers or maybe black licorice. The wheels, struts, and all other metal parts on the landgear mechanism all seem to have the same material. But most of those parts are painted/power coated a grey. Only the main strut (the hydraulic piston-like thing) would be chromey. airliners.net/photo/Air… airliners.net/photo/Bri… (airliners.net). If you really want to go to high level, try adding rubber hoses, and the really small parts. It’ll make it stand out. Also, don’t forget to rig those then. 
- Here’s the part where I get to mention the general lack of wear on the textures of everything. In this image in particular, there should be masses of ‘industrial’ dirt on the bottom side of this thing. I’m talking sooty, dirty water being splashed up from the runway. You’ll remember this thing flew New York-Paris most of it’s time. Aircraft have a condition known as rivet rash. Edges of areas, rivets, and the like, get a little bit of leaked rusty/dirty water under it. So those areas have a faint, darkish downward streak under them. en.wikipedia.org/wiki/F… (wikipedia) airliners.net/photo/Rus… (Airliners.net) <- a more extreme example of weathering.
Aircraft get repainted every few months, to maybe once a year. So they have at least a few layers of paint even if it’s only two coats of primer, and a topcoat. Point is that there would be bits of chipped paint here and there. airliners.net/search/ph… (Airliners.net)
The paint is also slightly ‘uneven’ or slightly unevenly faded: airliners.net/photo/USA… (airliners.net) Notice the black coat on top of the aircraft.
Another good example of subtle discoloration. airliners.net/photo/Fra…
Also, these external combustion Rolls-Royce engines weren’t exactly clean burning. Some of your strongest dirt effects would be brownish/tan smoke behind the engine, on the underside of the wing.
If you need some inspiration, some ‘targets’, take a look at these:
http://www.cantarel.de/hp2005/index.php?seite=display-3d-image&image=ec
http://www.cantarel.de/hp2005/index.php?seite=display-3d-image&image=boeing777
http://www.cantarel.de/hp2005/index.php?seite=display-3d-image&image=pavehawk
Wish you all the best, and I hope my wall-of-text get’s taken into consideration. 