AM 1510 and AM 1200 with their 50-KW transmitters are , in my mind, wasting energy, since their directional patterns are such that they go nowhere.
Not so...at least not exactly.
If you're looking at radio-locator coverage maps, it looks like coastal stations such as these are sending huge lobes out into the ocean, but they're not really. What you're seeing on the R-L maps is the effect of much higher ground conductivity over water vs. over the relatively poor soil of New England. You can see the same effect with stations such as WLYN, WESX and WJDA, all of them using non-directional antennas but all still appearing to throw much more signal over water than over land. (Even more dramatic is the 30 kW day signal of WMVX, ex-WNSH, on 1570.)
As long as you have large population centers in close proximity to salt water, this will always happen. It's not stupid, nor is it a waste; it's just the laws of physics at play.
In the particular cases of 1200 and 1510, their current night signals were squeezed in quite late in the game. Both had to protect much older class I clear-channel signals and thus had to put significant nulls to the south and west (toward San Antonio for 1200, toward Nashville for 1510, and also toward Sherbrooke QC for 1510). All you can do if you're designing a station like that is to put it as far to the south or west as you can get it while still providing sufficient signal level over the city of license. Sure, that means a lot of signal gets pointed out to sea - but what matters isn't what goes out to sea, it's how much population sits between the transmitter and the sea. That's still several million people in the case of both of those signals - and that's hardly "wasting energy."
It's true as well that 590, 850 and 1510 (and 680, too) were all designed to cover the metro Boston of the 1940s and 1950s, not the metro Boston of today. That's true of AMs all over the country, and there's only so much that can be done about it. 590's tightly hemmed in by WTAG on 580, of course. But even if you could find the allocation spacing to move any of those signals west - and then get zoning permission to build new AM DAs somewhere like Dover or Sherborn or Hopkinton (which will never happen!) - there's still a tradeoff: your increased signal strength in Metro West means lower signal strength in Boston and on the coast.
The Boston market, as it now exists, is simply too big, and the ground conductivity too poor, for any AM station other than WBZ to truly be a full-market signal. And WBZ, of course, has the unique advantage of being a class I-A clear channel that could perch on the edge of the ocean and blast all of its signal inland, because it didn't (and doesn't) have to protect anything at all beyond itself.
Another STUPID move: a "heritage station" (see above) giving up its call letters so as not to be associated with its past.
Aside from us geeks, who remembers WMEX? Even if you make the case that the original WMEX was still worth paying attention to in its final years, that was 35 years ago now. Someone who was 18 years old in 1978 is 53 now and already aging out of the desirable sales demos. And the 18 year olds of 1978 were probably listening to WCOZ or WBCN, anyway, not WMEX. Even the oldies revival of WMEX on 1150 was more than 20 years ago now.
"Heritage" in radio is a slippery thing. If you're not constantly keeping the heritage alive, it dies awfully quickly.