So... general concept, "Táim buíoch díot" is "I am grateful TO you" , as in I give thanks to you for your specific actions, or something like that. Out of curiosity, then, how would you then say "I am grateful FOR you", meaning along the lines of "You are one of the best things in my life"?
The correction: "You used the wrong word - I am grateful /for/ you" is inconsistent with the other "correct" answer above, "Translation: I am grateful /to/ you." The "Report" function should have an "Other" option to flag up errors such as this which are not covered in the list offered.
Just as in English, where "thanks" or "thank you" can range from a throw-away or even sarcastic remark to a very sincere declaration of gratitude, go raibh maith agat is a flexible phrase that can be used in a range of situations. People use these phrases in English and in Irish without really thinking about it.
"I'm grateful to you" is probably a bit more formal, or might be considered more sincere, but it really needs a "for" to feel natural - "I'm grateful to you for your help" - Táim buíoch díot as do chabhair.
Here are some examples from the NEID:
"I'll thank you not to mention this again" - bheinn buíoch díot ach gan é seo a lua arís
"we're really grateful to you for your help" - táimid an-bhuíoch díot as do chuidiú
"I'll be forever grateful to you" - beidh mé buíoch díot fad a mhairfidh mé
"I'm eternally grateful to you" - tá mé fíorbhuíoch díot