I was trying to think of some new ideas and details which could be added to a model, without adding a bunch of new/"upgrade"/more detailed parts from another kit or an aftermarket source. Basically, constraining your build (for the most part) to work with and improve what's inside the box.
Maybe these have all been done, but I like seeing things on models which set them apart from other similar models, without going to the extremes or spending a bunch of money on additional parts. Things such as:
1) Adding exposed/open headlights on cars with hidden headlights such as a '69 GTO, '70 Superbird, '67 Coronet, etc. I know these were sometimes optional (in the case of the GTO at least) on the real cars, but in kit form the Monogram '69 GTO Judge kit never gave the builder that option. Ditto for both the 1/25 JO-HAN and 1/24 Monogram Superbird kits.
2) I was considering scribing completely through the door and trunk gaps on the '69 Dart I'm working on, with the idea that once these panels are free, the doors and trunk panels wouldn't be made removable, but instead re-attached (possibly slightly askew to imply hinge pin wear), with the gaps backed up with black styrene strips to provide natural shadow lines without the need for "artificial" filling in of the gaps via paint or ink. I still think the gaps would nee to be narrowed to be more realistic after the panels are reinstalled, but I think it could work.
2B) A similar idea involves scribing through cowl panel vent slots, then adding a plenum area under the cowl, to allow for a a natural shadow effect. I don't think I'm brave enough to try that, considering how thin the cowl ribs are and how perfectly parallel the slots would need to be for it to look good, but I know I've seen someone use a photoetched piece for this purpose, so maybe that factored into my thought process.
3) It's often suggested to replace the overly thick kit supplied clear "glass" parts with acetate sheet or similar for a more realistic appearance, but has anyone tried thinning the kit glass by sanding it thinner? With a polishing kit in hand I think it's definitely possible, but is anyone crazy enough to try it? My thinking is that the kit supplied "glass" is designed to fit (though never is a perfect fit) the car/truck body, while you need to take extra steps to positively and securely mount the acetate, and ensure it stays in place permanently. Clear styrene is very durable, and much less prone to warping over time compared to softer, more flexible materials, but I'm not sure the styrene could be thinned enough to a scale realistic appearance without breaking while being thinned. Flat or nearly flat side windows would be easier than a compound curved windshield from a '57 Ford, but later windshields would be easier.
4) Thinned or removed moldings such as windshield trim is another area I've been thinking about. Using a '68 Camaro as the example in this case, and trying to emulate the real car's windshield trim, the thickness of the Bare Metal Foil should accurately replicate the thickness of the real trim, which means the molded in trim should be sanded until it's flush or the same height as the body areas around its perimeter. Then, BMF is applied, adding enough thickness to represent the real Camaro's trim. Now, I understand on real cars the windshield sealant bead is never perfect around the full perimeter, and thus the windshield height can vary in relation to the body's sheetmetal, but I think that variance is insignificant when scaled down by a factor of 25.
5) The "squishing" of tires to replicate how they look while supporting the vehicle's weight is another example of something subtle which adds realism but doesn't require any extra parts or expense. I think this would be one of that hardest things to do, as it would require a great deal of restraint and if you're working with vinyl tires, perfect application of heat. I've seen lots of junkers and beater will fully deflated tires, but I'm not sure if I've seen one with fully inflated, "squished" tires.
6) I think the tip for scribing new front valance panel-to-fender gaps on the 1/24 Monogram '71 'Cuda and '70 Challenger T/A kits is fairly well known, but this idea can apply to cowl-to-fender gaps and lower fender-to-rocker panel gaps (or lack thereof), too. The opposite applies to dutchman panel-to quarter panels also.
Now granted, #1 would require some donor parts, so that sort of falls outside the "keeping it within the box" idea, but it's close. I think I was going to try this very idea on a 1/24 '69 GTO a few years ago, and IIRC Marty (tuffone?) in AZ sent me some dual headlights to use, but my idea never got off the ground. Seeing this picture of a real '70 Superbird with its eyes open may have reignited the spark, and I think it's a detail which really sets the model apart, especially from other '69 Daytonas and '70 Superbirds which are rarely if ever seen with the headlights exposed:
I suspect the "squished" tires might be noticed by a few others, but the thinned glass and modified trim, if done successfully, might not, and that's kind of the point. For that reason alone it might not be for everyone, but I think it would be worth trying, and if you have picture of someone who's already done it...which is highly likely, as I freely admit my ideas above are nothing groundbreaking.
Better yet, if you have similar ideas, please share them.