I sympathise with them but I think its a lost cause. Royal Mail is struggling to break even, with a lot of the bigger companies using couriers instead of Royal Mail. The public would not take too kindly to another hike in postal prises to cover a wage rise.
To be honest, one day strikes don't really affect most peole I know. They may affect companies but (and this is no criticism of the individual workers) the service you now get from Royal Mail is so poor anyway that 1st class just means "quicker than 2nd class", you don't have a last post time - just the knowledge that the post will be collected at some point before 5pm etc. I haven't even noticed the strikes on the day, just when I get a larger than usual amount of post the next day.