I've been journaling since 2015, one text file per day and have not missed a single day. However, quite often the daily consists of the single word "Working.", so the bar is not exactly high. I usually write about what I spent my day on, and impressions about the media I'm consuming. I also collect interesting quotes and links. The longest dailies occur when I try to analyze my direction in life, progress with personal projects, the frustrations of a day job, and such. I originally started journaling as a form of brainstorming to help writing fiction, but I since moved that content elsewhere because its format clashes with the rest of the journal.

I sometimes read old entries randomly, but rarely find it enjoyable. However, every New Year's Eve I skim through each daily from the previous year and make a list of "all the things I forgot I did this year", and the list always surprises me very pleasantly with lots of things I totally forgot about. Honestly this alone makes it worth journaling — I feel really bad about not being able to reliably recall things I did prior to 2015.

Looking at the entries from the earlier years, my writing has definitely improved a lot. I always write in English although it's not my native language. I also like to write on paper but it makes organizing the documents a pain.

To answer the question, yes it has improved my life and I don't plan on stopping journaling.