I am using a mid 2012 MBP right now. I upgraded the RAM to 16GB soon after I bought it in 2014.
It runs fast enough to the point where I haven't felt the need to upgrade the original spinner HDD. If you have enough RAM using a slower HDD instead of an SSD seems to mostly effect the system boot up speed. I can run many Mac apps and leave them open without any issues. If they are running in the background there is no wait time to run them.
If you don't run large apps or like to have many apps open at one time on your Mac then you are probably ok with 8GB. Even if you run larger Mac apps the SSD will handle the page swapping fast enough so you shouldn't notice a negative effect with your running system performance.
I am a big advocate of maximum RAM in computers. I used to build my own PCs and I noticed that the systems with the most RAM installed tended to have less problems over time. Those systems seemed to last longer and the HDDs didn't seem to fail as often. If you leave your Mac on all the time you will notice that the amount of free memory tends to drop over time until the next time you reboot the system... It is sometimes due to inefficiencies in the OS... memory leaks, flaws in program code, etc.. Once your system starts page swapping to it's larger boot drive then it runs less efficiently... It can run hotter, use more battery power, etc.. Whether it's Windows or MacOS having more available system RAM helps alleviate those kinds of problems.
Therefore it really does depend on the user and how they use their Mac. From what you have posted about your Mac 8GB may be more than enough for your needs. If you ever get an itch to do another upgrade to your MBP then you could upgrade to 16GB (2 x 8GB) in the future.