Isn't it amazing what people think a modification does to their gun value?
If it was all that great, it would be standard or an option from most gun manufacturers.
Perhaps you should present that point to manufacturers, with aftermarket triggers, quality scope bases, quality scope rings, and extra magazines at the fore-front.
Then again, I can save you some time: They don't care.
They make and sell just enough to keep the average idiot happy. If someone wants a better trigger, they can get it elsewhere. If they want more magazines, the company will gladly offer them with a 300% markup. If they want better scope bases and rings, hit the catalogs/internet. If a plastic stock isn't good enough, Boyd's will have something.
And, some modifications and accessories are worth far more than your simple statement implies.
A few years ago, I started converting a ratty Marlin 336 .30-30 to .444 Marlin, before turning the project over to my brother (I had another, better 336-to-444 I was working on). He finished it, with a beer can shim to clock the barrel, mis-matched hardware, and custom-shaped, spray-painted stocks sourced from two different models. Total cost was under $300. Since the rifle made its way back to me last year, I've had three offers of over $600. Why? Because the work to make it a ready-to-go beater is already done, and it's still cheaper than a "proper" JM 444.
About five months ago, a friend in South Carolina sold a Hamilton Bowen customized Ruger Redhawk for $750 over what he had into it. Why? Because some people want it
NOW, instead of shipping the revolver to Bowen and waiting eight to twenty months before they see it again (
if HB will even take the work).