nahh. your ear can't be off. that's what linguistics is about :-)

however:
for
1. "The hotel has three rooms vacant."
the structure of the sentence is different than may appear...
three rooms is not modifying vacant... or measuring vacancy... the actual structure is something like
"The hotel has three rooms [that are] vacant."


2. "Kruger 60 is four parsecs distant."
this may be ok, but i suspect it's an effect of scientific jargon and not natural language... does the following work equally well for you?
"The Empire State Building is 4 blocks distant"

?
tx!

blessings! :-)