Great question - I'm new to the forum but your question is right up my street. Ive designed call centres for M&S, Tesco Bank, The Cooperative Financial Services, William Hill and many more. Unfortunately most if not all are in the North of England and Scotland. The only one in the South East is a small call centre I did for Thurrock council in Greys which I did through Vertex in 2005 which still looks great but wasn't designed to have the really big 'wow' factor. We had a nautical theme on this one with port holes in the doors and wave sea blue desk screens with alternating waves and shades. It looked quite effective but the client wanted something discrete as it was to be functional and didn't have visitors and attrition rates were low already prior to the refurb.
When I disuss with clients who want the wow factor I normally try to work out an overall budget and what we need to get within that budget. I then try and squeeze out of the budget as much as i can on the elements of the design that really make an impact and create the wow factor. alot depends on who needs to be wowed - is it staff to reduce attrition rates or is it visiting companies or potential clients?- this will determin where the impact needs to be designed.
As an interior designer i take note of many studies that show that how we perceive our space around us is influenced heaviliy on what we see at our horizon level when we walk around the space or look up from our desks - if you are looking for a low cost 'quick win' to improve your space - have a look at your walls surrounding you and any elements that in are in your 'horizon line'. Do these elements inspire are they well designed; are they well lit with interesting features? or as most offices tend to be are there walls that are dimly lit, no interest, windows covered in dull blinds; pin boards and white boards with no thought to graphics or interesting branding. If our horizon is bland or looks poor then our perception of that space is equally poor regardless of how great our workstation, chair, lighting is imediately around us. This is very important and something that is missed time and time again by interior designers within our industry - i think it's because a lot of office design work is done by companies who sell the furniture and design on plan which had led to a lot of bad designs.
At William Hill's call centre we printed full colour large dynamic images of sports related imagery onto wallpaper so we had entire feature walls with interest and then lit them. It had a huge impact and made a big difference to what was a tired building and interior.
There are so many things that can be done its difficult to discuss on a forum. if you want some ideas send me a message with your contact details and we can discuss further.
If you are going for a full refurbishement there are lots of great features that can be designed but it needs designing into the scheme straight away before you start otherwise it can loose its impact.
I hope some of this has helped