Detroit Auto Show 2015
The Volkswagen Cross Coupe GTE concept vehicle, a plug-in hybrid SUV Mark Blinch/Reuters

Volkswagen's long-serving and controversial chairman Ferdinand Piech has announced his resignation.

Piech, the mastermind of VW's global expansion and a towering figure at the German group for more than two decades, stepped down on 25 April after losing a showdown he had provoked with chief executive .

Almost 80% of VW investors expect the car maker's stock market value to increase after Piech's departure as it may help unlock greater earnings potential at the 12-brand group, a survey by advisory firm Evercore ISI showed.

"Piech's departure is good news for VW," said Evercore ISI analyst Arndt Ellinghorst, who raised his recommendation on the stock to "buy" from "hold". "VW has a better chance to turn itself into a more profitable and valuable business."

Empire-building at VW, which only a year ago took full control of Swedish truck maker Scania, should play a smaller role in the post-Piech era, analysts said, noting that Piech had appeared keen to buy Fiat Chrysler's Alfa Romeo brand.

Under Piech, VW bought ultra-luxury brands Bugatti, Bentley and Lamborghini, integrated Spanish volume unit Seat and raised its stake in Czech division Skoda.

"The sheer complexity of VW is starting to hit the wall," said Ingo Speich, a fund manager at Union Investment which holds 0.6% of VW preference shares. "There are numerous trouble spots at VW that urgently need to be tackled now."