I carry a few DX's in various states of wear, and now a couple of gstars. I use the beat ones for almost any fairway shot near water and all straight to turnover shots in the open (leopard for tighter areas and woods). I use fresher ones and now the gstar for when I need the most distance and control.
The past 2 years I carried an early 12x that was my primary distance driver. I just swapped it out for the gstar and I think it will stay out. My absolute favorite Teebirds were the old board-flat DX and 10x KC Pro's because they flip up perfect for me every time but are stable enough not to burn to the right hard. I have rarely gotten a newer DX to this point without it getting too understable soon after, but the Gstar at 173 is flying exactly like my last 169 10x that is isn't beat to death. As long as it holds close to where it is after the sharp flashing is worn I will be happy. The other GS in my bag is 5 grams lighter and mainly used for left-hand and flick shots where I want more flex available at lower speed.
Carrying a few of the same mold is never bad in my opinion. As long as you know what disc does what. I have improved my game massively by cutting down on the discs I carry and learning my favorites, but over time I am learning even more discs so I know where they can go in-between what I have, or if they should just be a backup. I usually only carry any "backups" when I am playing a new course, a water course, or a tournament.