I'm an amateur currently owning a Canon 700D and a few lenses (18-55, 10-18, 55-250 and 50 1.8 STM). As I try to do some stock photography, image quality is my main concern, and 700D has a very average sensor scoring only 61 at dxomark. I've heard dxomark ratings shouldn't be taken literally, but Canon APS-C sensors are known for poor performance for both DR and noise, and this is the case for 700D. I'm on a limited budget, so going full frame is out of my reach. Nikon APS-C cameras have about 10% larger sensor and don't have low pass filter, giving sharper images with less noise. I prefer Canon aesthetics more, but my main concern is image quality - do you think I should switch to Nikon or maybe the gains in IQ wouldn't be worth the cost (again, I'm selling stock photography, so with better image quality I could possibly sell more and cover the cost of the switch)?
The most important thing for stock photography is composition/artistic vision.
Next is proper technique which involves both the skill of the photographer and, for things such as night architectural work and most nature photography, proper hardware such as a sturdy tripod.
Next comes high quality lenses.
Only when all of these have been taken care of do minor differences in sensor performance matter. There are good techniques that have allowed many photographers to produce stock images of outstanding quality with far less camera than a Canon 700D.
Switching from one consumer grade APS-C camera to another consumer grade APS-C camera may slightly make up for some shortcomings in technique, but it will not make any material difference in the overall quality of your stock photos.
I doubt the sensor is holding you back (for the record, I shoot Nikon). Much more goes into good IQ than just the sensor: lenses, lighting, and technique are all huge factors in the equation, this is why DxO scores should be taken as only part of the decision process.
I think I would really consider investing time in a particular style of stock and refining technique on it. Given proper lighting, approach to shots, a good sturdy tripod, and careful balancing of ISO and shutter speed, you can get appropriate quality. People have been shooting stock for a lot of years with far less capable camera bodies than the 700D. Other techniques, such as bracketing and image stacking can do a lot to eliminate noise and increase DR and IQ.
Until you know, for sure, that the camera is what is holding you back, I wouldn't be looking to switch.
Instead of buying into new system you should invest in better lenses. Eg. you are interested in architecture - look into tilt-shift glass. Nature? Prime telephoto.