I wouldn't do it for a 52 Mantle because I've never liked that card and consider it grossly overvalued.
But with that being said I have sold a chunk of items a few times to buy a rare/expensive piece that I wouldn't normally buy and have had ZERO regrets.
There's 2-3 items that come to mind right now where if they became available I'd happily sell up to 80% of my collection to acquire them. For me it's always quality over quantity.