Sadly, I don't belong to a union. I can answer all of your questions based on several friends who managed to join a good union here. What car does my buddy drive? Why a rather nice Camry, with all the fixings. What car does his boss drive? Actually...a rather nice Camry, with all the fixings. What does the head of his union drive? A Sebring convertible; missing some of the fixings.
Of course, here in Alberta there are a few categories of Union. Some, (such as the TWU,) are complete piles of ass and failure and simply need to be purged from the earth in a firey cataclysm. Some, (like AUPE and CUPE) still serve a valid purpose and aren't out to "skim money from their members."
The difference seems to be public versus private unions. Unions of individuals employed by the private sector (with one or two exceptions) seem to do little anymore. AS you pointed out, workplace regulations took care of their needs moons ago. Some are still needed, especially in our mining and oilfield industries...but for the "average joe" they serve no purpose.
Unions for publicly employed individuals however seem to be very good and necessary. I don't know how things work where you are from but here we have public health, education and many other services. Were it not for our unions those teachers, doctors, nurses, policemen, firemen and many more besides would be working for minimum wage. Instead of the absolutely top notch services we receive from these individuals today, we’d have collections of poor, bitter, disenfranchised workers. Instead of our public services employing the best of the best, they would merely employ those who could not find work elsewhere.
I’d rather our police not become bitter and secretive like in the UK; jealous of the little they have, constantly afraid of losing it. Our firemen are chronically understaffed; to ask them to work at the poverty line would be beyond lunacy and so I am glad their union kicks our government in the ass periodically. Most of our teachers are overstretched, and it’s good that our unions work hard not only to ensure what id best for their union members...but the results are better for our children as well. (Mandatory maximum class sizes, as an example.)
I don’t know if a union is necessary in say, Sweden. They’ve got most things sewn up tight there. Alberta however is as American as a Canadian province gets. My provincial government was bought and paid for ages ago; they are constantly trying to privatise our education, health care and other social services. They are constantly trying to remove regulation on our resource industries. The only thing that prevents the decline of our civilisation into something resembling the US seems to be our unions.
For that reason alone; I hope they last forever. In most of Canada, we don’t seem to need unions. Alberta and Ontario seem to be the two places where they simply must exist. Many EU countries don’t have much need for unions, though some of the more recent joiners certainly do. Most of the second and third world nations however really require them. If you live in the US well...you’re already boned. That country is such a mess that unions aren’t going to help. It’ll take them fifty years for their social programs to catch up to even the recent joiners of the EU, and another fifty before they can weed out greed-based inefficiency. (Seriously, per capital health care spending is higher in the US than anywhere else in the western world, with significantly worse service and only partial coverage!)
Unions are not the answer to everything...but they have their place. Some, (like the TWU,) have overstayed their welcome and should be disbanded.
YMMV, depending on political beliefs, level of selfishness/greed/amount you buy into the dream the plutonomists feed us to try to keep us quiescent. YMMV also depending on geographical region and the social development of the populace/corruption of government.