I've been told the ES doesn't share any body panels with the Camry - although to me they're hard to tell apart. The TL is also unique from the U.S. Accord because it's based on the Japanese market Accord.
I don't think it's mandatory if you just want to sell volume mid luxury vehicles at modest prices, but I think you need bespoke designs if you want to compete at the higher luxury levels. Especially for Lincoln who doesn't have the luxury reputation of Lexus.
The bespoke suspension is just electronically controlled shocks and probably different springs - I don't think it's an entirely new expensive suspension. But either way I think it's money well spent since it will not only match or exceed the competition but it will further distinguish the Lincoln models from Ford models.