Matt Cutts - Google’s head of search spam released a video on the 28th January 2014 answering a question about long term established sites and their ranking changing.He changed the direction slightly.
He changed it, I feel, in a very positive way and recommended that owners of sites that are 'established' i.e. have been online for a long time take a serious look at their site(s)
Particularly, pay attention and see if it was a bit tired or lacklustre, and then to consider if anything could be done to improve the look and feel to bring established sites in line with modern standards in this area. This was a very positive way for him to emphasis the need to update, stay fresh, and make the site more interesting for site visitors and established clients.
His emphasis from that point of view was to see what you can do to help yourself keep your rankings and bring the site back up to a look and feel that is more in line with the new sites being created. Many newer sites having some stunning design features, which is where the question he was answering was originally pitched and are starting to infringe on the "established" domains in ranking.;
As we all know standards in the design of sites have moved very fast in the past few years. With the addition of all the different screens and sizes that sites need to be able to accommodate, it is a great time to update, get a fresh look and a responsive design site which will cater for all the new ways that the site is being viewed by your visitors.
Get your long term established clients looking at your innovation and being pleased to be associated with your business. Not to mention attracting new clients to your business. WIN WIN and you keep your rankings.