In the early 90s, what became the Probe was going to be the next Mustang. Even ignoring the FWD driveline, this original design didn't look anything like a Mustang. Enter the Mach 3 concept from about 1996 or so. This had some Mustang cues, but it was too much of a reach. Is that what I personally would want instead of the '05? Heck no.
It seems to me that cars with alot of heritage are the most ripe for a retro job... like Mini or Beetle, and possibly Mustang. Take the current Mustang (2004). It's catchy, has alot of design elements that tell you it's a Mustang, but was it ever all that special? I recall vividly when the first variant appeared in 1994. It was nice, but didn't seem to bring out the passion of the '05. This is subjective, of course, but I do think the original redesigns on legendary cars ('93 F cars come to mind) got stale quickly. The 350Z is not meeting expectations in sales, either.
I think one needs to step back and ignore whether something is retro or not, and take it for what it is. When you see the car, does it reach out to you? How many people buying Mini or New Beetle really lust for the original versions? Probably few. The new versions of the cars simply reach out to the market the way the original ones did. That's the key. If you step back and examine why the original Z car stirred the market, how it made people feel when they saw it and drove it, you begin realize why the new one is not as successful.