I'll say it again, a question of style.
I don't like the concept of the ACME Magic Artifact Co dropping off goodies. As this is the main thrust of the thread (although in chunks it has read very much like the Warlock gimping thread) that's where I stand. I, and most of the groups I've played with prefer a more roleplaying approach to problem solving, rather than just being presented with a queue of people to "talk" to. In these forums I've seen that described as blatant railroading.
As to sudden light have no mechanistic role to play, it falls in with a large number of situations that Mearls and Co have more than suggested be decided by individual DMs. Fiat is a strong element, I'd go so far as to say a necessary element, to fulfilling their original claims way back at the start to allow people to play in the style they want from Basic to 4e or even, the gods forfend, to allow 5e to stand as its own beast.
So, yes. At my table a sudden flare of light from dim to bright would give the party an advantage for a round or two assuming they were ready for it, when facing creatures that found glowing fungus a reason for wearing shades. I wouldn't expect that to be the case at everybody else's though.
At the heart of it, this is a roleplaying game with rules, not a ruleplaying game with rolls.
Although I am ok with a little bit of roleplaying for one single PC (and hence, one player out of six in our group), going down a PC rabbit hole (more than 10 minutes or so) can be boring.
I prefer my roleplaying being most or all of the team. I don't actually want to sit for an hour listening to a story about all of the things the one PC has to do to acquire a set of magical goggles. If I wanted to do that, I'd watch TV. I want to interact with a story and I want everyone else at the table doing the same thing.
I agree with Paraxis, a given player can do a lot of this offstage with the DM, or the DM can just go off and figure it out later. Let's get back to the real story.
Granted, 5 or 10 minutes, no big deal if one player takes the spotlight for that amount of time for some personal thing. If it starts getting to 15 or 20 plus minutes and the roleplaying starts becoming pedestrian (e.g. wooing the barmaid to get the info on which merchant to talk to), I'll start leaving the room for a snack, taking the dogs out, go to the bathroom, anything. If it's pertinent roleplaying (i.e. he is finding out about his magical goggles, and he is also finding out more info on the kidnapped shopkeeper), then it's all good.
In our last session, we took about an hour of time shopping. Zero roleplaying. We just sold the cart load of goods and the DM rolled to find out what percentage of net worth we got from it. We then took that stack of gold and everyone grabbed their PHBs and said what they wanted. We had a lot of gold, so it was a long list that took up a sheet of paper. Some groups split up every single gold piece. We do that for the small hauls, but for the big ones, we just go off and get what the group needs (which means what individuals like wizards need, like spell writing materials). If there is money left over, then we split it. The DM did not bother rolling to see if any given good existed in the town, it just did (with the exception of Potions of Healing where the DM rolled the max number).
If we would have roleplayed it out, it probably would have been four hours. Way too much time just to shop.
So yeah, I prefer "quality roleplaying" over "quantity roleplaying".
With regard to a magic shop, I tend to like them for the small common stuff. The PC fighter saved up enough gold over three levels for a +1 longsword? Great, go buy one.
But the really cool uncommon and rare magic items should rarely be found in a shop. The royals, or nobles, or temples, or armies, or wealthy merchants already snatched those up.
But, magic items exist. They have to come from somewhere. They are worth a lot, so there will be a market for them, even if in a given town it's a black market. Not having the ability for the PCs to purchase magic items makes the setting implausible and artificial. Commerce for magic items would exist because there would be a profit in it.
I also find it implausible that NPCs can craft them, but it is way too tough (time consuming, expensive, too rare of components) for PCs to do so. Meh. What makes sense is for PCs to be able to craft them, just like NPCs. It might require some significant effort, but making it nearly impossible is dumb in a game.
This is a game played by people to have fun. Let them have fun by buying and crafting magical items. At a cost, sure. But still, those elements should be in the game. Why make the game so restrictive? Meh.