Agile in the sense you are describing really has the wrong name. Agile implies fast; from Apple's Dictionary:
able to move quickly and easily; able to think and understand quickly
Agile should have been called Adaptable or some other name that has less implication of speed and more implication of accomodation of unknown or changing requirements.
No putting that toothpaste back in the tube at this point though.
Though this has the same problem as "cheap". People always equate "fast" or "quick" with "quick right now" and "cheap" as "cheap right now". There are enough examples in long-term projects that this is not true (though the converse is true, as well. And those problems which transist from short-term to long-term are just nasty)
able to move quickly and easily; able to think and understand quickly
Agile should have been called Adaptable or some other name that has less implication of speed and more implication of accomodation of unknown or changing requirements.
No putting that toothpaste back in the tube at this point though.