I've probably let 50+ go over the past 30+ years. Don't have any I regret giving up. But some of those springers like the HW 97k, AA TX200, RX-2, RWS 54 and the Titan SSP were sweet and I thought I'd be keeping them forever. But then the PCP scratch hit me and I was becoming less able to to cock & hold my springers.
If anything I regret NOT buying specific guns. SLR 98 mentioned in this thread being one of them.