And you admit to it? Btw, some people specifically do not say ashamnu more than once. But I definitely never heard of anyone lekatchila skipping pieces. Maybe you should consider davening with a slower minyan. After learning Mateh Efraim and associated Perushim I don't think you would want to intentionally skip any parts of Selichos.
I admit it. See attached. I also plead guilty to skipping some of the kinnos (from the ones not written by Rav Elazar Hakalir) such as some of the ציון ones if I find that one or more of the kinnos connects with me particularly , and I want to take it slow because that kinnah brings out emotions of the churban and galus. I find that preferable to rattling off all of the kinnos just to have gone through all of them. (The maharil did not say all of the kinnos).
By the avoda of Yom Kippur I had a hard time with the אמיץ כח piyyut. The language is difficult (along with some of the phrases such as והפר צווי כפתי) so I say the sefard version that is clear and allows me to understand and connect to what I am saying.
I think that many of us are just not willing to admit that we need work on our davening. In the fairly yeshivishe place where I daven on shabbos the reason the guys are running for the seforim the moment they come in, and spend much of davening learning, is not because they simply can’t tear themselves away from learning; its because davening is difficult for them and it’s easier to learn half the time.
We have to be honest that many of us are not where we want to be when it comes to davening. So we rattle off yotzros. And vehu rachum. And selichos. And countless other tefillos. Ideally we should all learn the beauty of davening and join super slow minyanim that allow us to say every word leisurely. But is that realistic? Two and a half hour shacharis on a Monday-Thursday of assures yimei teshuva anyone? (There actually isn’t physically enough time between sunrise and tzeis on Yom Kippur to slowly say all of the davening and piyyutim that many Kehillos say.) But that’s not the reality. We can select some parts to have more כוונה or we can resign ourselves to rattling off everything hoping it counts for having said it. I don’t think the latter is what we are meant to do. Obviously slower and more כוונה is the ideal we should all strive for, but don’t let the perfect be the enemy of the good...