If you are intent on using your slipjoints I agree that you should put your modern folders away somewhere where you can't easily get to them. If you can get to them you'll probably use them because they're more convenient and require less maintenance.
If your fathers and grandfathers had easy access to harder modern steels they would have happily tossed those old slipjoints in the trash. My father has gone his whole life without owning a cell phone and he talks on the phone much more than I do. Does that mean that I should limit myself to using a landline? I don't see the sense in that.
I've never owned a slipjoint that sliced as nicely as my Inkosi or PM2. I'd be interested to hear what slipjoints everybody is using that is so superior to anything a modern folder is capable of. I've tried GEC, Queen, Case, Rough Rider, Buck, Victorinox, etc. etc. etc.
Slipjoints are fantastic. They're pretty, they age gracefully, they're a ton of fun to collect, etc. However, if you find yourself reaching for your modern knife over your slipjoints it seems silly to try to force yourself to use and carry a slipjoint. I went through this myself when I first started carrying a modern folder. I'd carry a slipjoint along with it because I had some feeling of betrayal if I didn't. I've gotten over that now, and I usually just have my Inkosi on me. I still fondle and use my slipjoints around the house, and I still really love them. However, now that I'm carrying a modern folder I no longer feel the need to carry multiple knives around with me.