I upgrade when the new camera is significantly better for my needs than my old camera, enough so that it is worth the annoyance of having to "learn" the new camera (buttons in different location, menu different, grip a bit different....).
Lenses however - I don't need an excuse to "upgrade". Upgrading really means, get a lens with new focal length, tilt-shift, light / compact and good enough at f/5.6 - f/8 landscape lens for hiking, lens that is considerably sharper than current lens of its type, or other new capacity.....
Support and bags: well, we all are suckers for straps, new tripod heads with additional capacities, better flash bracket, etc
Lighting and modifiers, home-made and store-bought: where did that adapter go?