First class or not first class

Between us we'll be saving £475 on travel costs per month if we were to move to Greenwich.  This will be going straight into the mortgage as we'll be upgrading (in terms of house price at least), but I am tempted to try first class.  The new season ticket is £652 / year, first class is £980.  For a 10 - 15 minute train journey I think this is a bit much but would be fun.  Maybe i'll just do it in the summer months when it's hot and I don't want to stand with the oiks.