Latin is a huge influence not just on Irish Gaelic (which importantly must be stressed varies greatly from Scottish) but on all the languages across Europe. Take the Latin word for 'goodbye', 'adieu' and its French and Spanish equivalents 'adios' and 'au revoir' for one simple example.
There are many similarities with other European languages actually which is why many will notice similarities between Gaelic and Spanish. The ancient Celtic languages i.e. European Celtic languages (continental) and other European languages such as Galego and also because the Basque region was such a thriving Celtic region many connections are often made there. As well as similiraties between Irish Gaelic and the traditional Italian.
No-one knows for sure. What we do know is that there are some striking similarities, "how are you?" in Irish gaelic is "conas a ta tu" which is of course very similar to "cómo estás tú" "how are you?" in Spanish.
Overall though does it really matter if it is widely spoken fluently in Ireland? Given that the best English language novel ever written 'Ulysses' was written by an Irish writer (James Joyce) along with the fact the best playwright of the English language (apart from arguably Shakespeare who may or may not have been Irish

) was Oscar Wilde another Irishman I can't see the bewildering distress. Strikes me as something more along th elines of a blessing. Relax, just notch it up as another example of one of those other things Irish people do better than the English themselves

.
Having said that all my family can speak Gaelic. Just because you can't hear it doesn't mean that it isn't spoken. In a globalised world English (the growing prominence of Spanish in America and the growing popularity of Asian languages such as Mandarin not withstanding)is for practical reasons the language of choice especially in a small country like Ireland that has always relied so heavily on exporting its population and having to look overseas for work.
There are a growing number of very succesful Gaelic schools however and it is spoken just as frequently in remote country parts of Ireland as it is in Wales. Most Irish born citizens at least have a basic grasp of the language.