Planetside is a very cpu intensive game. While the graphic card certainly matters, you can get dramatic increases by keeping the same video card and getting a newer CPU(i just did this). Your video card is a bit older, so your results will vary. Video cards right now are almost impossible to find, and when you do, they are inflated to 50% and more beyond MSRP. With this in mind, you are probably stuck with that card for the forseable future, until the GPU situation is sorted out. Depending on on how limited you are fund wise, the best current option in my opinion would be to get an SSD. It will make the computer just respond faster overall. No, it wont increase your FPS by much, if at all, but there is no one component that really will. Even a newer card will be bound by your current CPU. So, with all that said here are my thoughts on upgrades you could consider.
Solid State Drive - SSD
Samsung 860 EVO 1TB SSD
https://www.microcenter.com/product/...id-state-drive
Obviously the most expensive would be the CPU/MoBo/RAM setup. Most things are on DDR4 right now, so even you would be upgrading all 3 together.
Intel Core i3 - $100
https://www.microcenter.com/product/...oxed-processor
MSI B460M PRO Intel LGA 1200 mATX Motherboard - $80
https://www.microcenter.com/product/...tx-motherboard
G.Skill Aegis 16GB - $57
https://www.microcenter.com/product/...6g---black-red
So, for about - $230 you would be able to replace all 3 components. Obviously, you could step up on the processor to an i5 for another $40-50 or so, but the above would be a dramatic increase in what you have now.
Video card? Not going to find one, you may want to consider used on ebay. Obviously this is a roll of the dice. I am currently waiting until things sort themselves out to upgrade mine. Below is an example, just food for thought
https://www.ebay.com/itm/XFX-Radeon-...oAAOSwGKJfzV1s
If you have any questions please don't hesitate to ask. I used intel because right now, bang for the buck in that range, I think its a great deal. You could definitely do something similar with AMD.