During one of my recent self-induced piano lessons I decided that I had given myself too much to practice in a 30 minute time frame. Actually, I realized this during my practice sessions, but during my lesson I made the decision to decrease the amount of things I practice during the week. I also decided that I needed to re-do a few of the pieces that I didn't get to practice as much during the week.
There's something to be learned here. Don't bite off more than you can chew. You'll only frustrate yourself if you try to accomplish too much in a single day. You'll also find that you won't make as much progress if you try to do too much than if you break down your efforts in to manageable chunks.
I feel that if I work on practicing well (taking things slow, correcting mistakes instead of playing through them, etc) I will get better faster and I've seen evidens in this pretty quickly. My sight reading has improved quite a bit and I make fewer mistakes, even on new pieces.
Hearing yourself improve is a great boost! If possible, record yourself so you can hear your progression over time. Recording yourself and listening back on it will also help you correct your mistakes.
If you find yourself not making the kind of progress you hoped for, take a deep breath and step back. Have you tried to accomplish too much too quickly? Pare down your project into smaller tasks and focus on one thing at a time. Really hone in on improving one skill at a time. It may seem small and tedious at first, but as you get better, you'll get faster and when you move on, preforming that skill well by rote will save you huundreds of hours later.