The first class on Greater Anglia outer suburban trains is intended for commuters to enhance the prospect of a seat. It's not luxurious at all. I would say no to the upgrade. Save your £14 and buy something more worthwhile.
On my many journeys on the line I have seen rowdy teens and gangs take over the first class compartments who have no tickets, so you may want to take this in to consideration if trying to avoid the scum. There's no guards on these trains and encounters with revenue protection staff is minimal.
Depending on what series of train is allocated to the journey, it will be either a class 321 or 360 - below is a comparison between first and standard class of both trains. As you can see, it's not really worth it, is it...?