Watty, Morgans tend to get modified by their owners; therefore, I wouldn't be too concerned about the switch to wire wheels from that perspective. Also, as Dave has said, it isn't irreversible.
Wire wheels are heavier than the other Morgan offerings but that doesn't mean the car in question hasn't been set up to handle the extra weight. If you are serious about it, what about getting it looked over by a knowledgeable mechanic (preferably one with Morgan experience)? This should help put your mind at rest.
