Even the use of 으려 has a "degree" to it.
If you are plain old "going caroling" you would just say it (or maybe use the future tense
하겠다, or leave room for fate to change your plans
크리스마스 캐롤링을 한다.
크리스마스 캐롤링을 하겠다.
크리스마스 캐롤링을 할것 같다.
I go Christmas caroling.
If you are expecting that "going caroling" will have some issue occur, or more likely using this to tell a story where something happened along the way to going caroling 으려 describes your state of on the way so that it might be interrupted.
크리스마스 캐롤링을 하려고 한다.
I am planning to go Christmas caroling.
In the past tense it's is more useful:
크리스마스 캐롤링을 하려고 하다가 다른 데로 가기로 했다.
I was going Christmas caroling but decided to go elsewhere.
As demonstrated in that sentence,
기로 is a degree different from
으려, in this case that minor difference between
If it is found by itself, as you suggested, it just comes out stronger - like some sort of Yoda speak where you purposefully shown your decision in the noun state.
크리스마스 캐롤링을 하기로 한다
Christmas caroling is what I do.
I'm doing it it's like
Doing it is what I am doing. Whereas
으려 might break down to
I plan on doing it.
으려고 하다 -vs- Past Progressive Tense
Think about why we use Past Progressive Tense. When something is happening but is interrupted or punctuated by something else, we need this to explain it.
I was going but met a friend.
This is where
가려고 했는데 친구 만나서 안 갔다
기로 -vs- Making up one's mind
It is very common to hear the phrase for
to make up one's mind (
마음을 먹다) in conjunction with
I made up my mind to go.
가기로 마음을 먹었다.
response to comments
Sorry, I tend to go for literal translation too often. 크리스마스 캐롤링을 하기로 한다 (depending on context of course), would most likely mean "okay i've decided (am deciding) to go caroling".
for your second comment, 크리스마스 캐롤링을 하기로 했다 is not that you went caroling past tense but decided to go caroling...so the caroling when is left unclear without context.
the third comment, sounds like a decision for the future. i never meant to say that it only works in the past. frequently, it seems, Koreans tend to say in a present tense that which (in my part of the world) we would always clearly represent with a past tense.
i think that is part of the confusion here that 참석하기로 합니다 sounds like a present tense decision where in English it would likely be phrased
It has been decided ...attend...etc.
one final, less complex thought
trying to do, attempt to do it, have intention to do it
plan to do it, decide to do it, definitively strive to do it