Given the limited window on picking up all the stretch goals and game expansions (which certainly are not in the original) I think if you really like Fief you would do well to pick up Fief 1429.
I agree with you.
There are many little improvments in new version : ergonomy is really better, with title counters instead of cards for example.
New and better illustrations for counters (troops, castles and cities), revised boardgame, etc.
But the answer of the question is yes, because nothing prevent to play with the new rules with the previous version.