Not all products are for all people. If you foresee a need to recover a large amount of data all at once, then glacier's not for you. If you might occasionally need a filing from 6 years ago, then glacier would be great.
Amazon starts to charge you extra anytime you exceed restoring 5% of the data.
If for example you save all your tax-related documents in Glacier, then you are audited then the accounts department or the government will want all the information. Not 5% of it. Not 10% of it. Everything. At that point Amazon will have you over a barrel, because getting the data out at a reasonable time frame will cost exponentially more than dripping out the data over the course of 20 months.
Are you sure about that? I haven't worked with tax litigation specifically, but I've worked with e-discovery w.r.t. e-mail and I can assure you that no one ever asks for all the e-mails sent by a particular company over all time. It's always a matter of asking for the e-mails sent by or received by a select group of people, over a fairly discrete time period. For something like this, a Glacier store might make sense, if it was coupled with an online metadata cache stored in e.g. S3.
The government basically comes to you and says they think you owe X, and you have to prove that false to their satisfaction. The more data you give your CPA to work with, the better.
Legal issues, at least in the US, do not have those requirements.
I have had situations in the past 12 months where recovering past data would be worth >$1k for the right 100k of data.
Isn't one way to get past this... increasing your data usage by 20x? If OP used less than a $1 a month, then if he uploaded $20 of junk data, he can get the 5% original data back "for free". Sure, it's $20, but it beats out $150+.
Though it's hard for me to imagine having so many categories of unrelated, useful and important data.