Fair enough. I see what you are saying, and indeed the tracking of the effects over the years for when things become obsolete or less interesting and such, is way too much a pain in the ass.
Presenting this userfriendly though, could just be adding a certain year per item, when things become outdated. Maybe work with colorcodes like in engine and car designer. Green is brandnew, yellow is normal to be in the car at that certain year, (orange: lasts only 1 - 3 years) red would mean that its outdated, like a cassetteplayer in 2004 for example.
When you add years of outdating to every individual item, you don't have to track their effects that heavily. You could make a couple different, static, models for those, like:
- Gradually decrease from 19xx to 19xx/20xx
- Stay equal over the years, until a new part is invented that makes this one obsolete(Cassette/CD player)
- Stay equal over the years, until a new part is invented that then gradually decreases it (airco/climatecontrol, Wipers/auto-wipers etc.)
- Gradually decrease to a level and then become equal (Radio for example)
- Stay equal from the point it gets introduced, as current tech doesnt replace it yet (Electric windows, for example)
And probably a couple more. This way, with like 5 or 6 models, you can cover pretty much all the gear. Targetgroups then always have 1-3 wishes to put in a car, changing by the era, to boost sales up a bit if your car actually has (one or more of) these things.
It doesn't always have to be complex. This can be a simple addition to the game which touches more than just the designer and how much 'p3n1s' a man has down there

This could actually be a nice dynamical and more in-depth part of the game, which weights as much as designing an engine or car does.