I am in a similar position to the OP - only been in a few years, never going to have a massive pension because of that, no legacy payments to be taken away, no childcare issues to need to finish early etc etc.
But I will be voting YES for industrial action and the main reason is what RM are hiding behind the word "flexibility" in the offer. The proof of this is in the way I have been swamped by them with messages and mailings - what company has ever taken such action to get their message across (while hiding the real message)?
RM have talked of a "race to the bottom". That race is being made by RM itself in their determination to compete with other companies who don't have any real rules to abide by. The courier companies don't have to potentially deliver to every house every day and for a fixed fee. Their staff (who they love to compare us with) don't have to prepare and deliver door-to-doors every day - an one column on the average frame has 80 slots, 4 d2d means you are preparing over 300 items before you even start on the post - it may only take a few minutes, but RM think that anything which takes a few minutes actually takes no extra time. I see items doorstepped by couriers on a daily basis, and the great thing is that most householders immediately blame RM for everything delivered to them! There are loads of other reasons why there is no comparison between RM and other delivery companies.
When I joined RM there were still afternoon packet delivery duties. RM took them away to save money, now their future plan is based on the ability to be able to deliver packets later in the day. What sort of turnaround is that, and who had the great idea? At my office around a third of postie have the job because they needed to finish in the early afternoon for childcare reasons, what are they going to do if 'flexibility' turns the job into a regular 9am to 5pm?
One of the mailings from RM said to think of the community. That is the same community that Royal Mail Group took away Post Offices from, the same community that has had later collections taken away from post boxes - often boxes without a date tag to know it has been emptied. The same community that posties no longer have any time to be part of by having a quick chat with someone who never sees anyone else all day.
They talk of best jobs - that came in a week when my office failed to get everything through IPS on every day!! A week when we cut off on a Tuesday!!!
I am not a left winger, I have never voted Labour and never will - for many, many reason. But this isn't about politics, its about whether you want some form of a decent job, or to be expected to be "flexible" with no real idea what that will mean.
To repeat, I'll be voting YES.
. Don't go moaning to your union rep or work colleagues when Sunday becomes a regular day either. I despair 
...If you vote no, cancel your CWU subscription because if you aren't going to back them when there's a national fight you don't deserve their help when you have your own issue.