There are some figures here: http://www.ireland.travel.ie/aboutus/facts_numbers.asp
Of 6.2 million overseas visitors in 2000, roughly 3.5 million came from Britain, 1.45 million from “mainland Europe” and 950,000 from the US.
Note that these are figures for all travel, not just tourist travel, but so far as promoting the circulation of euro currency is concerned the distinction between tourist and business travel is probably unimportant.
The total spend by overseas visitors was about £2.1 billion, of which £873 million was from Britain, £578 million was from mainland Europe and £557 million was from North America (i.e. US and Canada).
So visitors from the eurozone are both more numerous and more signficant in terms of what they spend than visitors from the US.
As a customer of an Irish bank, if I use an ATM in Ireland there is a small fixed charge. This is true whether I use an ATM of my own bank, or of any other bank.
But if I go abroad and use an ATM, the charges are a lot heavier. There may be chunky fixed charge which would impact heavily on small withdrawals, and there may even be a charge expressed as a percentage of the withdrawal (which isn’t, obviously, a foreign exchange charge but might as well be). The charges will vary depending on which bank’s ATM you use in the foreign country.
The “justification” for these charges is that, within Ireland (or within France, or within Spain . . .) the banks will all be members of a common clearing system, and can reconcile all their payments to one another’s customers fairly simply and quickly. But when I draw money from an ATM belonging to (say) Banco Santander, and Banco Santander wishes to debit my account with (say) the Ulster Bank, there is no clearing system to which they both belong and the cost of processing the transaction is greatly increased as a result.
(A suspicious person might think that it had something to do with the banks having lost the money they used to make on foreign exchange business, and wishing to make it up somewhere else. But it would be uncharitable to suggest that, so I won’t.)