When do YOU upgrade to blu ray or 4K?

[Spaceace77]

I received a Sony DVD player as a X-mas gift in '99. Started collecting New releases on DVD on day one with Detroit Rock City. Didn't upgrade to blu ray until 2011 when I also upgraded to HD tvs. And then in 2018 I purchased an 82" Samsung QLED 4K,along with LG 4K blu ray player and Yamaha 4K receiver. I've watched dvds on my new setup and can really tell the difference. But I'm not one to spend $20-30 on a new 4K release of a movie that I already have on DVD or blu ray. The only time I purchase movies that I already have is when it's an incredible leap in video audio improvement over the DVD or if it's a cheap price (from DVD to blu ray). I did,however, but the Criterion edition of A Hard Day's Night when I already had the blu ray version of it. But price was half off, and it's The Beatles. SUPERIOR picture over the one I got from Amazon in 2013, which has French language on cover. My question is this: how many times will you purchase the same movie?