Yeah, if you're doing CPU-based rendering that can fully utilize additional cores and threads, a CPU upgrade could also be useful. Depending on the software, more cores with SMT (Hyperthreading) might potentially be more beneficial than getting higher clocks with fewer threads though. The higher thread counts of an AMD Ryzen system might be good, even though they won't clock quite as high. Or, on your existing motherboard, maybe a locked i7-8700 for a bit better per-core performance, albeit at a higher price. You might also need to replace the stock cooler to keep an i7-8700 boosting to its full potential under heavy loads though.
Ryzen processors with a similar 6-cores and 12-threads cost significantly less, though they don't clock quite at high, and you would need a new motherboard for them.
As for the graphics card, an RX 570 offers performance close to an RX 480 / GTX 970 / GTX 1060 3GB and only about 10-15% behind an RX 580 / GTX 1060 6GB, while being around 50% faster than a GTX 1050 Ti. You can currently find RX 570s new with a fresh warranty for around $150, even some with 8GB of VRAM, though you might need to send in rebates to get those final prices for some...
https://pcpartpicker.com/products/video-card/overall-list/#c=392&sort=price&page=1
They do require significantly more power under load than a 1050 Ti though. You might need a PSU upgrade for any of these CPU / GPU upgrades if the one in your system happens to be relatively low-end. Do you know what model of power supply you currently have?
It's probably worth shopping around a bit, unless you really need to buy through eBay. At the very least, you probably shouldn't buy a CPU from a seller with a ( 1 ) feedback score though, like the listing linked to in the previous post. : P
Again, I think your biggest immediate gains (especially for gaming) would come from the graphics card upgrade though.