I track my neighbors in an Excel spreadsheet. I track days as friend, gifts/ days, level increases / days. I also track the times I was unable to send a gift on a friends list as well as whether I could not assist them for lack of timers on exposed in their city.
I had reached level 125 on Windows phone but lost it all for lack of portability. I am now on Android / FAcebook. I am 113 days into the game and am at level 86, helper level of 25, and have 46 purchased and 7 assigned friends.
My current threshold for deletion is a gifts / days percentage of less than 80%. I do not delete for receiving unwanted gifts. Even my best of friends may sometimes go a couple of days without a gift. The 80% threshold began closer to 30% but continues to rise as my level increases due to the better quality of neighbors you are exposed to at higher levels.
I will consider sharing the spreadsheet template if there is an interest.