I still use merc and hospital discount regularly; keep them. Ore values is good when you're out of money at the end of a map but you have a ton of neodymium ore from caches that you will never smelt. I use mine boost on the occasional map in which I need to smelt fancy bars, but usually I skip those maps anyway. The rest I do not bother using anymore.
oh dude, time warp to legendary, ASAP, you can live without some of those. burn mcb, tmb, and whatever you have a lower level of (i.e. army camp boost and use fodder to get a lower level army camp boost to rare quickly)
Given your rarer artifacts, what I would immediately say is that you can sacrifice Efficient Smelter, Money Cache Boost, and Item Values. Both Efficiency artifacts aren't usable because the percentages are WAY too low to give you any benefits. I hope you found that one and didn't upgrade it. Otherwise that - in my eyes - would have been a huge waste. MCB is easy because you already have a better one of this type, there's not even a question here. Item Values is debatable, but you have a better (soon-to-be-Legendary) Alloy Values and most Markets have at least one Alloy, so for a Market-Merc-Strategy Item Values isn't strictly necessary. As a fourth sacrifice I'd probably choose Mine Boost. But only because I never use my Mine Booster despite the money it could probably generate (I never bother with calculating the exact profit). But I really can't suggest the one you would upgrade as this most of the time is a personal decision. But given that I've identified three artifacts that are mostly expendable - unless you wanted to keep one of each, but in that case you wouldn't have asked - my suggestion would be to upgrade something and not keep them all as you probably won't use each of them even if you kept them all.