G'day Charlotte,
(have I mentioned before I love the name "Charlotte Webb"?)
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While I agree we would probably be better off without {{spoiler}} tags anywhere, I can't say the same for infoboxes. The real problem there is inconstant formatting from one template to the next, and that there are too many specialized ones, and in some cases nobody can agree on which one should be used (see Paderewski). Ideally it wouldn't matter.
Infoboxen can be incredibly useful for at-a-glance statistics, e.g. countries, the dates of a monarch's reign, etc. They are more often annoying. Occasionally we can see infoboxen that are just ridiculous (I don't have a real example off-hand, but imagine if the [[Superman]] article --- which I haven't looked at; I hope it doesn't --- had an infobox with sections like "Special powers" and "Supervillain enemies").
The problem with infoboxen isn't that they exist. I support the use of infoboxen in many areas. The biggest problem is that they are very often used in places where they're unnecessary or even frankly silly. That's a bigger headache than problems with formatting, consistency, pigeon-holing, etc., although I agree that they, too, are problems. Infoboxen are not inherently problematic, but there are too damn many of them and most of them suck.
For now the best approach would probably be to limit the ability of wikiprojects to annex articles of debatable relevance. Probably I'm as annoyed by talk page banners as you are by infoboxes.
Talkpage banners, ugh. The number of times I've seen an edit to a previously-untouched talkpage of an article I've written, and gone, "Whoopee, someone else also cares, maybe they're even now posting a note containing the missing piece of info that will turn this into a Super Article!", only to find it's just some dickhead from WikiProject Texas claiming the article as their own.
For the most part, though, apart from an endless succession of talkpage banners from various projects, my articles don't get much attention from outsiders, I think because they're too obscure (let's see someone from WikiProject Texas, WikiProject Cars, and WikiProject Australia fight it out over a Victorian State politician who used to own a petrol station before running for parliament!). If anything, a little harrassment from the WikiProjects would be welcome; I'd know that, a) someone actually reads the articles, and b) if I leave them alone for twelve months (which I'm very close to having done now) someone else might improve them.