Haha this may happen to me also.
Anyway, I pulled the trigger on a Zebralight H600w today. I decided that instead of going with a primary light that used a standard battery configuration, I'd go with something high powered, with numerous modes and insane runtimes and output. It's a bit heavy, I figure 3.6-3.8oz for the package, but I wont be carrying extra cells for it.
For a backup I'll have either a single cell AAA or AA light (I'm leaning toward the Eagletac D25A mini (0.77oz without a cell), which is single AA and has outputs high enough, and run times long enough to cover a pretty serious bailout if I needed it, which I'll put a high capacity lithium primary in (Energizer Lithium AA 0.5oz)
My current Petzl Lamp weighs 3oz with Alkalines in it, could drop it a bit with lithiums, but a set of backup cells would be another 3/4oz in lithiums, so I'm at nearly the same weight primary, with 10x the output potential, many more modes, huge runtimes, fully regulated output, better color rendering, the ability to clip to my pack straps for night hiking, etc.
I'm also expecting I'll enjoy the beam quality a lot more, since I can't stand the Petzl's color, spill/spot profile, and glare.
I'm fairly certain I'll be able to work up a diffuser for better flood profile in camp if I feel I need to also.
In the end, I'm not saving weight, but I don't think I'm adding it either. I am losing the ability to find a battery at a gas station if I forget to bring one, but that's a risk I'm willing to take. I am however I think, increasing versatility, utility, and user happiness, god willing. I'll add the redundancy back in (which a single headlamp, regardless of battery type doesn't have if it simply fails) for the 1.25oz penalty, of a backup light with a standard battery type.
I've got plenty of room to add back in utility and still maintain crazy low baseweights, so the marginal net gain looks like a win to me here, and I've got other options for SUL/XUL pack lists, but those arbitrary number exercises no longer hold much appeal for me.