Study books and play less. Grab some good books, such as advanced tactics books, middlegame books and endgame books. For openings, design a repertoire that you enjoy to play and get the necessary books on your choices. As you grow in knowledge, your games will be greater learning experiences because you'll be implementing your new perspectives and techniques. I say this because I got the impression from your post that you're playing a lot of games and hitting the wall. You can overcome this through study.
Getting benefits out of long games
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So I know online ratings are inflated, distorted etc, shorter games especially so. But, i've gotten to the point where my blitz rating is 'decent' by my own arbitrary standard but, in my opinion, my level of play is really not much better than it was when I was rated 1400 or so.
I would like to improve or at least feel like I'm playing a bit deeper better chess and I always see that the way to do that is to play longer games. Ok, but what does that mean, 10 0, 15 0, 60 0?
And what am I trying to get out of that?
For instance, when I improved playing blitz I would quickly run my opening through chessops, which has a bit of a commentary on the openings to tighten up my openings so I could have a good foundation for the fun in the middle game. Are there things I should be practicing within these longer games or just having the ability to think in more depth?