Personally I'd rather have a word presented in humility along the lines of "I think God is saying..." simply because it makes it clear that the person presenting it does believe the word is from God but it's also clearly inviting me to test the word. The "Thus saith the Lord" proclamation sounds very high and mighty, and to me would suggest that the person speaking it expects it to be accepted as is.
Sometimes things can turn out to have a far bigger impact than expected. Years ago I was scheduled to lead the Bible study group I attended, and what we usually did was a more detailed study of the Scripture used for that Sunday's sermon. When I read the Scripture in question I thought that including the following verse would be relevant. When I read the Scripture before the study, as I read the extra verse one of the ladies in the group started crying - it turned out that one extra verse was just what she needed to hear at that particular time. Was that a prophetic thing, was it a fluke, was it something else? It's the sort of thing that could easily be argued any which way but ultimately the lady in question got the comfort she needed, when she needed it, and in a safe place where she could express what was bothering her among people she knew and trusted.
It's certainly not something even remotely worthy of reopening the canon of Scripture, it's not something that anyone outside of that group could verify, but it's back to the idea of God moving one person at a time rather than having some guy standing on stage trying to reach a million people at once. And from my perspective as the study leader there was no sense of "Thus saith the Lord", no sense of believing God had a specific word for someone, just thinking that the passage made more sense if that one extra verse was added.
