Are you considering doing this, or just thinking out loud? No problem either way, but if this was something you were planning on doing, I'd leave the salts out this round. Assuming you can get your mash pH correct with the dark malts, and assuming your water has got enough Ca for the yeast (at least 50ppm), I'd brew this batch as is. If after this batch you think the bitterness is a little too pronounced, or it needs a little more depth, then you can think about tinkering with the minerals. Someone else on here brought up the point that I liked, that the trouble with matching a particular city's water is that you don't always know what the brewery did to treat the water after it entered the brewhouse. Now Dublin might be a little more well-researched than some places, but for starters I wouldn't try to match Dublin water. If you think your sulfate/chloride ratio is a little high and you want to supplement with some CaCl2, I also don't mind tinkering if its well thought out. But I can't think of a reason why adding carbonate to change your hardness would effect the flavor in a positive way, outside of pH considerations.