Our last big milestones were our 40th birthdays.
Me: We planned afternoon shopping/window shopping in Bath followed by a meal. I could get anything I fancied whilst out. I bought one item for £60 I think. He may have bought me flowers but I can't remember now.
DH: We went out of a meal, I bought him some favourite chocs. he may have bought some electrical gadget and said it was for his 40th but, again, I cannot remember.
I think we just both got to the point where we realised that if there isn't something we particularly want then we are not interested in spending money/cluttering up/going on a trip just for the sake of it. We treat ourselves to things (by mutual agreement as we have completely joint accounts) when we want them.
Life over the last few years has been dominated by work, bring up young children, doing up the house and paying off the mortgage asap. Under those circumstances having to make a big effort for birthdays would have been a chore tbh and we would much rather give token gifts and mark the day quietly - I think that is more about energy than money though.
I can see this changing within the next couple of years though as, hopefully, we will have more time, energy and money to jazz life up a bit (which has become quite habitually dull on the whole). Financially, we are very secure now but in our drive to achieve that I think we have lost a little of life's sparkle and we both are starting to appreciate that it is going to take some effort to get it back.