Flip the question around.
When do you buy new gear/upgrade existing gear?
- When your current gear isn't enough to help you achieve your goals.
Yeah, pretty much this.
My gear isn't really limiting me right now; my "vision" and my skill at lighting, set design, pose direction, and retouching are my limiting factors.
New gear won't make a difference that's noticeable to my clients or subjects. Photographers might notice a difference, but impressing other photographers is very low on my list of priorities.
I could get incremental improvement by upgrading my aging 24-70 to a 24-70 vII. It's not as sharp as it could be.
I could get some OK improvement with a 135L or 85L. Or even a 85mm f/1.8 might be fun. But I already have those focal lengths covered with my extremely reliable and sharp 70-200 f/4L, and the results won't be markedly improved over the results I'm getting with that lens. Might get better bokeh, I guess. I don't need a shallower DOF.
I could get a "different" lighting look with a huge parabolic umbrella. Different isn't necessarily better, and my style tends more toward edgy, hard, dramatic lighting anyway. (still, this is one of the things on my shortlist)
I think my next purchase will be a Vagabond - so that I can take my higher-powered strobes out of the studio.
Also need to replace some aging & broken cheapo lightstands with some sturdier ones.