I personally don't hold grudges long, at least if the other person is willing to apologize, or won't hold a grudge against me. Of course, I won't forget what has happened, but I'm not very emotional person, and holding a grudge requires lots of negative emotions I think.
I do have a great memory. Just few days ago I was talking with a long time friend, and I noticed myself saying "Hey, you told me that already 10 years ago, no need to repeat yourself."
Dominant Si has also given me an exceptional sense of direction. I
never get lost. It's like having a Google Earth inside my head. So, I wouldn't call dominant Si just being "troublesome". It's just kind of double-bladed sword.
But I can't help myself from recalling the "good ol' times" from my past from time to time, and mourning what I have lost (possibilities, etc). But acknowledging this, I can push myself forward and tell my dominant Si that "Only direction we can go, is forward. And only in the future we can be something that we are not now". It helps... but I just have to keep doing that actively.
Throwing away stuff that reminds the me of the past has also helped. I bet you other Si's have plenty of stuff from the past, for the memories' sake.

Do yourself a favor, and hide them!
