I have never come across anyone being "blocked" from doing Irish research at Irish research locations.
I am Dublin based which gives me an advantage to accessing records and I have never had a problem at any research institution; in approaching cemeteries, churches, etc. the only problem I have encountered in is looking for a baptism record of a child that was adopted; I have always felt there was a notation that I was not given based on the conversation I had, I also needed a reference from another parish before I was given the record.
What may have happened is, that the people that you refer to, while on a short break in Ireland, were really being told "finding information in Irish Records is difficult and time consuming and may not happen in a short break, hiring someone to complete the task may be more beneficial and rewarding"
You can spend a day going through records and still not find what you are looking for or hit the jackpot and complete a branch of a family. Irish records are scarce and mainly paper copies, although this is rapidily improving. To do research yourself you need time; you need to know names and variants of the name; dates of birth with bands of error and the parish a person came from when looking before 1900.
See in Ireland Resources :
http://www.rootschat.com/links/0gas/ If you create a basic tree of your family, and fill in as much as you can from on-line records and family stories/history; use this to make a list of the parish locations you want to research and specfic names you will find your research will be easier and more productive.
I hope that this helps especially as most places here are welcoming and helpful, but they will be realistic if your search will take longer than your time available