Usually I'll only buy a re-release if it's a re-make... as in, there's been enough time since the original release(s) that there's a significant graphical upgrade and/or new content. Sypro on PS4, for example, I bought. I don't own any version of the Last of Us, but if I had the PS3 one I wouldn't bother with the PS4 remaster- it's a one generation difference, in generations that aren't that dissimilar. Not enough of an upgrade to warrant it.
I do buy a lot of content upgrades, since you can usually get the better version cheap. FF15 Royal Edition for $20? Horizon Zero Dawn Complete for $10? Yes, please! I'm not a big buyer of DLC, so it's often cheaper for me to just get the disc upgrade. I also usually know someone who doesn't have the game I can give the older copy to as well.
I'm often tempted by compliations for space reasons… the Devil May Cry HD collection, for example, has often tempted me becuase I could get rid of 3 discs from my PS2 collection & save some shelf space. Haven't done it yet though- the first DMC was a big deal for me, even got the guidebook, so I've got a nostalgic connection to that specific copy.
More than anything else, I double dip when digital titles get a physical release. I love my hard copies, so I practically feel obligated to get the physicals... plus, they're usually a cheaper release, so the combined total of the digital & physical is often only around $40. A number Id've paid day one if it was an option for a lot of these games.