I'm very interested in this post as I have a rear flare that is beat to hell...
I have mine "close" to minimize filler, but recently have been considering replacing it since the filler would then go on the quarter panel body, which seems to me would be easier to shape (since, you know, flat) rather than the lip...I am also worried about longevity as I plan to drive my car as often as possible.
EDIT: To the OP, they sell replacement panel for just the flare....FYI
eventually a 1969 Mustang Fastback--been in hibernation since 2011 due to school...
Now the time has come to resurrect her once and for all!
Currently on a body cart with a finished undercarriage.