I think it happens with many things, not just photography. Doing anything for longer periods can result in a reduction in interest. I think with photography I experienced a big slowdown after 2 or 3 years or so.
Don't force yourself to do something. If you're not in the mood, you're never going to be at your best anyway and that might create a negative feedback cycle. It sucks, I suck, why bother?
I found revisiting old favourites helpful. For me it was my local park. At my peak I'd visit practically every other day. Now it is more like once a quarter, so it is fresher and different every time.
I never found more kit to help much at provoking interest. It is a short term thing, and the initial interest wears off after a while. It does of course open up new possibilities, but if it can sustain is another matter...
_________________Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.