I mix and match a lot too, especially with BYOC. I think 3 or 4 times is probably the max I've used any kit.
I do have kits that I haven't scrapped with yet, but I also have kits that are go-to kits that I use over & over again
I mix and match, but one thing is certain , over 50percent of my scrapbook pages has a least 1paper from Amy Wolffs mega solid packs , I own them all,they are the most versatile papers out there. There are a few favourite Lynn Grieveson kits too,that seem to sneak an element or two into most pages,Birdseed and light me Home are the most used, and Forresier too,plus some of her patterned papers. , NBK Romance or Romantic,plus any of her floral ones ,and I really wish Kate Hadfield was still here, because her 9to5 ,Book worms, and also All the Everydays kits have to be my most used of all time, when it comes to single elements. The kits I bought and never used....let's not talk about them....a fair few, enough said.
I have bought kits that I've rarely used, but on the flip side, I've bought kits that I've used over and over. I'm not a "kit scrapper" ordinarily, so sometimes I use multiple kits on one layout.
I delete 80% of the kits I get after one use. To be fair, they are almost all CT kits so I'm not paying for them and I might feel differently if I had bought them all. I sometimes use Christmas kits over again in my yearly Countdown to Christmas album. I have one favorite designer that I keep all of her kits no matter what so a few of those have been reused but otherwise... nah. I do have favorite element packs & alphas (and some of those are more than 10 years old) that I will add to pages. Now that I have my new laptop (and once my EHD is repaired), I'm looking forward to setting up biancka's (not sure if she posts here or not?!) DigiScrap Catalog program so I can do more mixing and matching on my pages.
I have used one kit 6 times with no mix and match. But I too will mix and match and have used items multiple times.