tl;dr: it's not thankless, but it's not exactly an awesomely compensated profession either - there's lots of hidden shit teachers have to do/provide that should count against their compensation.
I'm often asked how we can possibly spend that much money on her class and it's a little bit complicated. While maybe $500 goes towards supplies such as pens, pencils, paper, notebooks, recorders and other basic implements we also spend money directly on the students. My wife typically buys every student a book for Christmas, we supply everything to holiday parties etc. Each year my wife spends another $500 or so on new wall hangings, new books for her library, teaching aids, resource books and more. The majority of the money however is spent taking care of the students in the most need. 100% of the schools students are on the free and reduced lunch program and the school is classified as Title II which means a dinner program is also provided to the neighborhood. Each winter we end up buying a large number of warm jackets, boots, gloves etc. In a neighborhood with 85% of the families living at or below the poverty level you wouldn't believe how much of a difference small amounts of help like that mean to the students and their families. My wife once had a student break down in tears when he received a winter coat. He told her that now his mom didn't have to worry about it and could pay the power bill. At Christmas we buy gifts (clothes) for the students that aren't included in the district wide program for the "underprivileged".
We certainly don't have to spend any of that money however my wife is there for the children and not for the money.
As for whether the summer is paid or not, so what? Your wife earns $54k/year, she just doesn't work all year.
Your quoted salary also completely ignores the fact that teachers in most states get benefits (e.g., defined benefit retirement at age 55, gold plated health care) which are vastly better than average. Teachers get more fringe benefits but less wages. Cry me a river.
Every salary'd job that requires a degree that I'm aware of gets benefits, and the benefits most school systems have are NOT better than average anymore. I pay less for health care, and have better retirement options at my private employer than any of the local school districts. We don't have a pension/retirement benefit (other than 401k), but school districts around here are laying teachers off and not hiring new ones because they don't have the money to pay them in the first place.
On top of that, most other professions don't require you to provide your own work supplies (ie: you get a paper to print reports on, pens/pencils and notepads, etc.), while teachers must purchase all of their non-textbook, non-furniture educational materials. Library of books, reams and reams of paper for work packets, colored paper, art supplies, science project materials (we've spent hundreds on various plants, moths, butterflies, etc. for life sciences experiments). Buying even paper and pencils for 72 kids over the course of a full school year is a non-negligble expense, especially at the salary being paid.
The TUS is a random sampling of Americans, the report in particular is the same data restricted to teachers. But I'm sure you can do a better job of sampling by asking your wife and her friends than the BLS can by calling randomly selected people.
Regarding benefits, it varies from state to state. You may be unlucky and live in one of the few states where teachers can't retire at 55 (i.e., retirement benefits which are 2.8x better than those of normal employees, ignoring completely the costs of defined benefits). Most states, however, give ridiculously good fringe benefits to state employees at the cost of some wages.
Also, many professions involve purchasing various goods and services. Doctors often purchase medical supplies, consultants purchase equipment (laptop, etc), I purchase books, most people in banking purchase expensive signaling clothes (can't get promoted if you don't look the part). Really nothing unique here.
http://web.missouri.edu/~podgurskym/articles/files/fringe_be...
http://www.bls.gov/opub/mlr/2008/03/art4full.pdf