For the first part, it depends on your point of view regarding the game, level 50 -60 doesn't offer a great deal, and yes after 60 yes you have to buy or win the keys, in order to get the bonus hero points..

Thanks.

To be clear, then, after reaching level 60 the hero advances by acquiring hero's keys and does not need any further experience points?

You need experience and hero keys

OK.  Thanks Monke.

In my particular case I suppose it will prove academic.  Experience comes easily enough but it is going to take a year or more to accumulate the remaining 450 hero's keys I need to attain level 60.

Sorry I wasn't  clear, yes you still have to collect the experience points, you just can't earn them without the keys to open the next level.

You have to decide if the bait is worth it.

The carrot may look appetising, but by the time you catch it, is it wizened, or just not big enough?