This is an opinion.
Realistically speaking, internal code quality matters more when you’re making something that people can modify and extend. Meaning an open github asset. If you’re making a project for asset store, then you’re designing a product instead and thats’ different.
(opinion) In this scenario, people won’t, in general, hack internal code (because they can’t redistribute modified version, so there’s no point), or even read internals, and you largely need to design clean user-facing side. That means gui if this is bunch of components/windows, or API if it is code/library. Regarding “people spending money on something bad”… there are a lot of awful code in assets in general, as not all people designing them are professional programmers. In general, clean user facing side should suffice. In contrast, internals can be lovecraftian, because people will try to reach YOU to fix their problems, and as long as you can make sense of it and are available for contact, that’s decent.
Additionally the point is to save user’s time and money. For example, programmer’s wage in USA seems to start at $30 per hour. A decent programmer would be able to replicate absolutely anything currently available on set store, but the catch is that it will take time, and time is money, and lost opportunity cost is involved. For example, said programmer comes home to work on his pet project, and he needs a leaderboard. He can make one himself, but let’s say (for the sake of argument) that it will take him 2 hours from start to finish. That’s $60 in lost opportunity and 2 hours of lost time. Now let’s say that there’s an asset that does what he needs and it costs $10. IF the asset works as intended, the programmer can buy it, and save himself 2 hours of time, and spend $10 instead. That, in my opinion, is the role of asset store.
On more complex system, cost to replicate skyrocket. Something like Final IK or Gaia can take 1 or 2 months of full time work (that’s assuming the dude in question already knows what features he wants, meaning no research is involved. Cloning takes less time than initial work.), and with the $30/hr guy that’s already thousands of dollars of lost opportunity cost. So for an US programmer rather than trying to implement those systems by himself it makes more sense to just buy an asset, even if it is not under open license and even with the risk of the asset becoming unsupported in the future. The situation can be a bit different if the programmer in area from significantly lower salaries, in this case the dude might decide not to pay $100 for IK, and just jury rig a replacement tech.
So, in my opinion, if you’re publishing for asset store, and your assets are code, that’s your role. Allow someone to save time by paying money instead of reinventing the wheel.
Like I said, that’s my opinion, and that’s how I see it.