From what I can tell, all the extra upgrades to memory and disk space are substantially more expensive than if I’d just buy them on the market and insert myself.
Other than essentially gifting Purism some extra money out of goodwill (appreciation of their great products) or a tiny bit of added convenience, am I missing some other potential reasons to upgrade directly on the website?
I don’t think so. I’m pretty sure it’s just there for convenience, which in turn provides some extra cash to Purism.
That is why I purchased my upgrades there. Because of the importance of path dependence when a company is small and trying to grow, I figured I could pay a bit extra. Obviously not everyone can or should do this. But since I really want to see a linux ecosystem flourish, I think of the extra cost as a social investment.
Yeah, same. I am happy to pay a premium for all Purism products in order to help their mission succeed.
my concern is where i pay EXTRA on my customs TAX because i go over a certain import limit and that i do NOT want to do !
this is me writing from the EU space.
if you are ordering in the US then this might NOT be a problem for YOU !
it all boils down to what each state/zone/customs-standard (if there is such a thing …) are applied in your area and for what type of ‘goods’ they apply to.
for instance, in my area importing under 20 Eddies is nothing, but over it starts going out of your pocket … over 4000 Eddies it starts being a drag …
Yes.
Not everyone understands the technology well enough to buy the right components themself. Talk of LPDDR4 and NVMe and … just causes eyes to glaze over.
Not everyone is confident enough that they can install the hardware without breaking something (and the smaller / more confined the space, the harder it can be).
Well besides helping to keep the lights on around here and helping to pay the salaries of the devs that do work such as; Pureboot, Librem 5,The software stack for the Librem 5 phone, and other software and hardware projects.
While other vendors might have hardware that is compatible, purism has to provide hardware (ram, storage units) that is compatible. And that Purism has to previously test to make sure it works with the laptops/desktop/phone Purism sells.
put that on the suggestion list for upcoming blog-posts ! 
“How our team tests Purism hardware”
that would mean we would have to clean up our desks for the pics!