It certainly is not a bad idea, but it does carry some risks.

Sometimes the additional trauma of treating a tooth will
'wake that sleeping dog' (mediocre root canal).  Cutting
off the old crown is usually simple enough, but if you want
to retreat the root canal to be more sure of long term success,
that post is going to have to come out as well.

That is sometimes a tough job to do without damaging the root.
If the post comes out OK, the retreat on the endo should be
successful.

Just putting a new crown over the old work carries the risk of
having to take off the new crown in order to try and retreat
the root canal at a later date.

Worst case, you lose the entire tooth and need an implant or bridge
(which could happen at any time anyway with an 'iffy' endo).

Not an easy call,
D

Just do it yu only live once and to live wit an ugly mouth is
revolting I am a NY Dentist