Cool. 
I think you are on the right track if you want to improve rating.
The stonewall attack (or setups) is fairly complicated and certainly of higher positional understanding than most all players under 1000. My guess (without looking at your games) why you haven't been improving is because:
a) you do not do game analysis to find mistakes to prevent them in the future.
b) you learned an opening by move sequence (like stonewall) and apply it to many situations where better moves could be played. I've personally fallen victim to this too. I know my openings so I like to transpose into lines I know well if my opponent plays oddly, but this isn't always best I've been learning. By giving them this option (or steering them into a transposition), you may be missing "punish" moves and ideas for their play or silly move order.
c) You need to experience more patterns and ideas. Tactics obviously help with this, but so does experimenting with different openings or trying other different things.
Too often, players want to improve but just continue what they have always done. If improvement hasn't been present, then changing things up may be the key, so I applaud your first step.
p.s. If you want, we can play some unrated games in the future and I could give you my feedback. Obviously, everyone has their own opinions (so I won't be offended if you take my thinking with a grain of salt). However, I personally find sharing chess ideas with others beneficial to both parties involved because exchanging of ideas exposes both sides to new patterns and themes.
I just decided at the beginning of 2020 that it was time to start to working on my rating. So my first goal was to find an opening that was recommended as being very instructive.
So I chose the Ruy Lopez. After using this opening for about a month now I can say that it has taught a lot about the power of central pawns, pinned pieces, piece activity, and reaching decent endgames.
I have clawed myself up to 950 on blitz and will begin transitioning over to slower games so that I can form better development habits and understanding.
Other wise I’ve began to piece together all of the ideas that I’d previously absorbed but never effectively put into practice. By using the tactics trainer I realized that visualizing a series of moves was very important. I really saw improvement after a member here recommended to a newer player that looking over your blunders and mistakes using the analysis tool was good. I’d always done this before but what I realized is that I never tried to improve on the ideas that create those blunders. So I began looking at every blunder and mistake in my games. I ignored inaccuracies. Many of my blunders are hanging pieces and visualization issues. Like not noticing I still have a bishop on the board tucked in my back rank. Or that my opponent is forming a discovered attack in the back corner while I’m pushing a pawn somewhere else. My first goal was and still is (cuz I’m still working on it) to eliminate blunders and mistakes.
Before I felt bored and lazy about “exploring” a series of moves before making them. I’d just move because it felt right or because I’d seen some pattern that looked similar.
But analyzing is extremely important for me and I’d always taken it for granted. I also like ideas that involve luring an enemy piece into a spot where it can be pinned and then attacking the pinned piece. Forks are also great. Fast development, sacrifices, and double checks are definitely what excite me the most about the game. I have silman’s complete endgame course and am going to attempt to understand those endgames since it has been suggested that the Ruy Lopez can lead to trading pieces, doubling enemy pawns, and large pawn majorities. I want to take advantage of that if it’ll help me push my rating higher.
TLDR I got a little better. My rating went up. Ruy Lopez is fun. I enjoy analyzing chess, and the challenge of chess is fun again. I want to improve. If you think you’ve peaked you’re wrong - try to find your weaknesses and improve on those first. You can Improve!
Dunno if this is the correct section, but I wanted to share my progress no matter how little it might be. Maybe it’ll encourage some of the people that have played for a long time but haven’t improved.