Does this come up in research/discussion, acceptable or not?

Sure. Many books will feature personal experiences of authors. If there is a historical discussion on TV, it's not unusual to have people involved in the studio etc..

However, from a neutral perspective, you are just one witness like any other witness. While you may have priviledged access to your own memory - and therefore find it especially convincing - you are still to be regarded as good or bad evidence as any other witness. You can err like other people, you can be biased like other people etc.. All the usual souce critique would still apply.

What could help, would be something like a written account of your experience (a diary, a report, a statement). If you recall events years or decades after they happened, your value as a source will decline (again, this is source critique 101).

The value of any source greatly improves if it is backed up by other evidence. If you get into an arguement and just claim "I am right, I was there, I saw it with my own eyes!" - then you are not very convincing. If you can point at other evidence and can support it with personal experience - that's a much better way to go.

Does the usefulness change if you are/were an expert in the subject you personally experienced?

Yes - to some degree. An expert witness is generally of higher value then a layman. But expertise alone is useless if other conditions are not met, eg. is the witness reliable in general, biased, etc.. - again, all rules of normal source critique apply.