I don't think it giving +$3 or +$4 solves the essential issue: This card is powerful for non-trashed BM when opponents don't have hand-size attacks, and it is useless when they do.
Minion, Margrave, Militia, Ghost Ship, Cutpurse, Goons, and Followers shut down this card hard.
How do you mean? I'm not sure I totally agree with this. I assume the reasoning is that it could turn your next turn into a 2-card hand instead of a 3-card hand. Well, Tactician turns your current turn into a 0-card hand, and that's still worth playing. Basically it's worth cannibalizing one turn if you can get enough of a boost out of the other. And with +$4 from a single card on that first turn, you can. No other Dominion card can guarantee +$4 on a single turn (without cannibalizing the rest of the turn, like Vault and Secret Chamber). Even if that first turn is attacked, Merchant Banker-Copper-Copper gets you a Gold, lucrative for a 5-card turn let alone a 3-card turn.
As for that 2-card turn, it's a far cry from a 0-card turn. You'd still have your two strongest cards (as opposed to average cards, which is why Militia'ed turns tend to be way better than Outpost turns), and with a +$4 earner in your deck, having $5 and $6 cards in your deck is likely. Mountebank + Gold? Library + anything? Best case scenarios, admittedly, but my point is that Tactician costs more, penalizes you more, and makes no guarantees on what the "good" turn will get you.
Rinkworks, adding a +$1 is not a flat increase in value of $3. A Workshop that gained $1 would probably still only be worth $4. $2-4 and $5-7 have a huge gap between them and a much smaller gap among them.
I acknowledged that the cost scale isn't linear. The higher the price, the larger the gap. However, this is also true of how many coins a card gives you. There's not a lot of difference between +$0 and +$1, because a terminal +$1 is still a terminal Copper, insufficient for building your economy beyond the $1.6 per card needed to get a Province. In other words, giving Workshop a +$1 still doesn't help you boost your economy to Province-buying levels.
It's different when you throw a coin onto Village to make a Bazaar -- because that's a cantrip, and it consumes neither space in your hand nor an Action to play. In other words, it
always raises your average card value. If your deck was nothing but Platinums, making an average card value of $5, adding in a Bazaar will
still raise your average card value, because what that Bazaar is worth is not just $1 but $1 plus whatever the card draw will give you on average -- which is $5!
Now, we are admittedly not talking about a cantrip here. But we ARE talking about +$ levels far beyond the $1.6-per-card threshold for building your economy. Above that threshold, additional coins become a huge deal. +$1 and +$2 is a massively larger jump than +$0 to +$1. It's why we have a lot of terminal Silvers and not so many terminal Coppers. Terminal Silvers build your economy and work toward Province-buying power. Terminal Coppers don't. It's also why we don't have very many terminal Golds -- the jump from +$2 and +$3 is massive and would be overpowered in normal contexts. At +$4, we're at stratospheric levels of income. You'd need a stratospheric penalty to justify it. "Discard a card next turn" is just about the weakest penalty possible, so often not a penalty at all.
Let's compare to Mandarin, a terminal $3. It's tough to compare, because the on-gain effect is a weird thing. But once it's in your deck, it's a terminal $3 (worse than $4) that drops a card from this turn (worse than next turn) by putting a card on your deck (
much worse than discarding) and costs $5 (more expensive).
However much you think Mandarin's on-gain ability affects its power level, does it really compensate for ALL of those things?
Rules note: What order would you get things if you had both this and a Wharf out?
You'd get to choose the order in which you resolve the "next turn" abilities of any Duration cards in play.