Corporate design for consulting company

Design details: We are a consulting company in Germany, specialised in fast and sustainable changes. We already have a basic corporate design (logo, colours, Word and PowerPoint templates) but

(1) It looks and feels 'selfmade'
(2) we have some creative people who tend to play around with designs

So what we need:

(1) corporate design, streamlined, based on the existing elements
(2) ongoing service, available for our creative people - every time they have a new idea or a new need - can approach and get a solution in line with the corporate design
Ideas for the visual style: vistem.eu
Extra notes: German language would be very useful but is not a necessity