Over the past year, I've parted with two basses that others would have chosen not to sell for "sentimental reasons."
The more recent was my Peavey T-40. It was my first real bass, and I got it in 1978 when I was 13.
I weighed and weighed the decision...I could see the clear and immediate value of selling, but heard other people say I would regret it. What it came down to for me was that I simply didn't use it and I was unlikely to ever truly use it again. Given that, I couldn't make a decision to keep it come out on top. Searching my mind, I also can't see where I'm attached to things purely from sentiment. It's just not there in any significant way.
Will I regret it later? I really can't imagine the scenario where that would happen, but who knows...but I'm sure I'll survive if my outlook should somehow change. There was also some satisfaction in realizing how jazzed the new owner (who is actually going to play it) was about getting it.