Well, if your photographic tool chest needs some more things to put into it, get the shiniest, glitziest bauble you can find. I know guys who have every power tool made nicely arrayed on their garage wall, complete with outlined positions and a key light shining over the whole showcase. But they don't actually use the stuff to make things. And they obsess over the latest double-bore titanium coated 57 degree 1/16" drill because they "need" the best equipment.
Uh huh.
Or, you can learn to use your equipment, get to the point that it is actually holding your creativity back, and then you'll know what you need to get. But don't let me hold you back if you're trying to help the economy get moving - it needs people to throw money into it.
Personally, I buy stuff when I can't get my existing equipment to do something and I have enough knowledge and experience to know that there's not another way to get it done. My last purchase was a 10 ND filter because I wanted very long exposures and my existing filter set just didn't allow me enough light absorption to use the very long shutter speeds I wanted. The last piece of major gear was a flash meter, about a year ago, because I was trying to reduce the number of times I had to adjust multiple off-camera flash power levels by chimping.
I'd echo the suggestion that if you want to "improve" your photography, then figure out what area you want to be good in and spend your money to get the books or courses that will teach you how to be good in that area.