At breakfast with two friends the other day, I realized I was talking to two people who had been at least as many rounds of decluttering as I had -- and they each had significant regrets about specific things they had purged. Oddly, it was usually purging craft-y/decorating things that caused the problem. After reducing acres of fabric to a much smaller pile, they had each had situations arise (that could not have been predicted) that a particular purged portion of the pile would have been perfect for (and neither felt that asking someone for similar items from their as-yet-unpurged pile of craft items was an acceptable substitute).
So that was interesting. I could think of two items that I regretted getting rid of, neither did I remember _specifically_ choosing to purge, but rather that I hadn't been able to find them when I wanted them. One was a turquoise sundress that was perfect when pregnant with T. that would have been equally perfect when pregnant with A. -- but was nowhere to be found. *sigh* That still bothers me. I've never seen it again; I probably really did intentionally get rid of it, possibly because it was showing a lot of wear. But I wasn't able to find the particular style when I was pregnant the second time, which was a bummer.
The other item I was unwilling to admit to in person and am only willing to admit to now because _I JUST FOUND IT_! I didn't get rid of it at all. When I was probably in my late teens (probably either 16 and just baptized as a JW or 18 and just graduated from high school), my cousin S. gave me a very small ceramic tchotchke, and it's one of a vanishingly few items of its type which I kept. I love my cousin S. (and would love to re-connect with her, as I think she's now permanently Out of the religion, and helping a LGBT student group in the school where she is a teacher, which I find profoundly awesome in every way), but that's not why I kept the tchotchke. It's a bookshelf. It has a cat on it, which is sort of a negative, since I've never had a cat (allergies), but I do like cats, and I dearly love cats on bookshelves (Twice Sold Tales in Seattle was a lovely place to go and pet cats while looking at books and conveniently near good restaurants with full bars to appropriately set the mood). I found it in my memory/photo box along with my sister's and my clay sculptures from elementary school. I had been thinking I'd love to put that tchotchke in the curio cabinet with the spoon and a few other odds and ends, but had no idea what I'd done with it.
Which is all a very long winded way of saying, wow, I really virtually never regret the things I get rid of, and even when I do, I probably haven't.