I agree with both Awaclus and dondon here. The player count could definitely have an effect on your perceptions, and groupthink is a thing too. Playing with Platinum and Colonies actually makes engines
more viable, because the extra source of strong VP makes the game longer, giving the engine more time to become unstoppable.
Having more players makes engines more difficult because of competition over engine components as well as how fast the non-engine players can drain the VP piles together. 1v1, the non-engine has a more difficult time ending the game before the engine can come back and take the lead. There is also the fact that Big Money strategies
can get lucky and win despite being inferior overall; having more players just increases the chance that one player hits some optimal shuffle luck.
That said, yes I understand can trip trashing is a hugely helpful kickstarter to the engine strategy. It does not, however, mean you can't have a good $4 card (hospital). The extra action on hospital means you will try and play it to play engine components (if you have no other +actions in hand) and will therefore start self-destructing your engine once it is built. It's almost like a tempter and is going to be a dangerous card to keep playing if you're relying on the +actions. However, it is actually quite a boring card anyway and I can see why Donald has never produced it, it's real interest in my set comes from the overpay to remove plague tokens ability. What would people think about:
Hospital $4+ - ACTION
+1 Card. +2 Actions. Discard one of your plague tokens. When you buy this you may overpay for it. For each $1 you overpay you may trash a card from your discard pile.
You can have a good $4 card, sure, but that doesn't mean you should have cards that are
too good. Hospital would be in that boat. As we've tried to explain, Hospital is very comparable to other cantrip trashers like Junk Dealer and Upgrade. Which of them is stronger isn't important (I think Hospital would often be stronger, but others have disagreed already and that's fine), but they are all definitely in a similar class. Hospital is very clearly a $5 card.
Your notion about Hospital self-destructing does not follow from its optimal use case. Even though it is a village, you shouldn't treat it as such. Its primary use is as a trasher, just like Upgrade and Junk Dealer. The +actions are just a nice little bonus that can help you out, letting you get more terminals earlier before you invest in other villages. Likewise, the +$1 from Junk Dealer is just a nice little bonus that can sometimes help you afford a card you otherwise couldn't. The mistake is in underestimating the value of the +actions, or overestimating the value of the +$1. The big thing on those cards is still the cantrip trashing.
On your new version of Hospital, I think it sounds OK. I would actually suggest dropping the overpay entirely, or maybe using the same overpay you had before. Just make Hospital a plague-cleanser through and through.