Personally I would never be without a valid passport- but I travel a lot - and I cross a border several times a week (between France and Switzerland) - perhaps OTT but I have 2 passports and 1 identity card ;). But as others have said, a passport serves so many other uses anyhow.
My big worry about your post is about you recently travelling without health insurance and only EHIC card. This only covers you for the emergency part of treatment, and no repatriation
If you had an accident, heart attack, stroke, etc - the costs would be massive for continuatin care then specialised repatriation with medical staff in attendance, etc.
Remember the woman on the news this Summer- who had a stroke in Turkey whilst on holiday- and only had an EHIC card?! Of course in her case, she was not even covered for the emergency part- as she was not aware Turkey is not in the EU! It just does not bear thinking about.
Mind you, on a happier note- my mum's last visit to the UK was for our eldest's wedding when she was 90. When she gave her passport to the Border guard at Luton- he said to her 'I am sorry Madam, but your passport has expired by several years'- she looked at him from her wheelchair and replied 'young man, at my age those things are no longer important - I am going to my grand-daughter's wedding' - he smiled back and said 'hope you have a wonderful time'. Wonder what would have happened if her tone of skin had been a bit darker and she had come from somewhere more 'exotic' than Switzerland.