Stiffer leather might last longer.
I don't mess with my leather goods anymore by putting the odd treatments on them. The one and only thing I use these days is Obenauf's LP (Leather Preservative). The LP can keep the leather conditioned without really "softening" it like saddle soap might.
Whatever you do, keep in mind any holsters you soften will likely only get softer and floppier with time, and you'll likely not be able to re-stiffen them in the future.