Well, the good news is you like your neighbor and you take care of each other. That makes for a good slip no matter the problems.
As to your Garhauer cleat, why can't you use a indelible marker so that you can put it back in the same position when you return? No different than racers/cruisers that mark their genoa cars postiions for different wind speeds. Saves time and guesswork and easy to fine tune from there.
I too make sure that I have extra lines aboard in case I have to dock somewhere else in an emergency. They can be old lines, but they still work for emergencies. However, it is so much easier if you can leave lines on the dock that put your boat in the same position you like without adjustment. Quicker/easier!The only line I always take with me is the spring!
Your third reason is why a spring line works for you. It forces the boat over to your pier and keeps it away from your friend next door.
With the lenght of your slip it may be easier for the spring from your Garhauer cleat to run outside your lifelines around the end cleat/post on your dock, and loop forward over your winch.
Before you go out next time set up the spring line and snug it up to where you want the boat to end up. Start the engine, put the boat in gear, and then remove the bow and stern lines one at a time and see what happens. A little turn of the wheel will move the bow to port or starboard and you will stay against the dock at mid ship.
I had a guy with a boat similar to mine ask why I did not have problems docking when he was having a fit with his boat. I showed him Capt. Jack's system and how I used it. He told me all the reasons it would not work for him( same port tie slip, very simialar boat). I said to everyone their own....good luck. After three more outings, and two hard landings, he came back and asked if I would help him figure it out. We rigged the spring in the slip, walked him through the physics of it, and then went out and came back in 4 times. I did the first landing, he did the next three, and not once did we hit anything. The only problem now is his slip neighbors don't have the same entertainment value they once had.....but their boats are safer!