How long is a piece of string ? Depends what you call a “big improvement”.
Yes you will get an improvement but your not going to double your FPS, probably more like get a 10% to 20% FPS bump depending on the flight.
The other option for people with enough space for a screen is build a mini-ITX gaming PC. My current PC is the size of a shoebox and only has a 450w PSU but runs a i9 9900K and a RXT3070 reliably with no issues.
As you can see it is a wee bit cramped but it works fine.
SG13 case modified to offset the SFX PSU about 20mm rearward to avoid kinking CPU hoses
450 watt PSU that I originally intended to upgrade to a Corsair SFX 750w but it seems to cope fine with MSFS so I did not bother (it definitely would not cope with a stress test or serious overclocking but who cares)
9th gen i9 9900K
older 8th gen Asus motherboard with BIOS upgrade for 9th gen
32GB DDR4
Zotac RTX 3070 (one of the few 3070 that would fit, most are too wide or too high)
Arctic Liquid Freezer II 38 mm with 2x 120mm fans, amazing performance for a 120 AIO, performs more like a 240 AIO, keeps the i9 down around 55 to 60 degrees when gaming