If the site wide liks are helpful to the user, branded and nor anchored with gaming text it can be followed. However, if the links are not helpful to the user I would not add them.
1)Start with relevancy... Will this link help anyone? Y or N
2)Is this page quality? do they follow best Search engine practices(Panda/Penguin)? Y on N
3)Are they active? do they have any social media interaction? Y on N
If all three are yes then get the link. I would recommend using a no follow tag if the link is below the footer. If the link is above the footer and all three of the above are yes then you can link it.
Only use an exact anchor if it looks right for the user, otherwise use your brand. Tip: I would use the brand just to be safe and keep the exact key phrases around the link. Search engines read around the link as well.