But there are tons of awful cards in Seaside! There's Pearl Diver, Embargo, Explorer, Island, Pirate Ship, Haven, Lookout, Smugglers, and Navigator!
Pearl Diver, Navigator: These cards would be ones I'd replace, except, I couldn't, just as I couldn't rename Harem; they depict real people. Why not offer those real people new better art on their new card, you ask? That sounds good to me, and I thought it would get Harem renamed, but it didn't.
Embargo: I like Embargo fine but would make a new similar card in order to not require special tokens. But wait, Jay has a pile of those tokens in a warehouse somewhere. This was not actually doing anything for him for years.
Explorer: They can't all be the best $5 ever.
Island, Haven, Smugglers: Haven is fine. Island is sweet. Smugglers is my favorite card in the set.
Pirate Ship: I'm with you on this one.
Lookout: I might not do this card today, because casual players mostly don't like it. Experienced players know it's fine, sometimes you get Lookout, and it probably doesn't trash one of your Provinces. Anyway it's borderline.
Another thing someone can cite from the time machine post is that I don't like that there are two junkers costing less than $5. It slows down heavy Seaside games. People don't like that Sea Hag is a pure attack so it would be the one to replace. Probably with an interactive non-attack, since people also like attacks in general less than anticipated.
But this ship has sailed (get it). I looked at the other sets a year ago, did any sets want new cards other than Dominion and Intrigue. Seaside came the closest, Prosperity was a very distant 4th. Well there's Alchemy, but the basic way to change Alchemy is to not do it. It does have fans so it's not like we have to take it out of print, but revising it would be a very poor use of time, given that solving the speed issue would never solve the "it has Potions" issue. Hinterlands has enough cards I want changed, but they all want to be the same card only changed, which isn't on the table; we can't offer an update pack with "Fool's Gold now has no reaction" and such.
Anyway I looked at Seaside. The biggest positive things would be to get rid of Embargo tokens and use the coin tokens on say 3 cards. Seaside was made without tokens so I was not trying to make sure they were put to good use (when Prosperity was delayed due to Alchemy, I had time to add two more VP token cards to it). As I said, it was going to be a while before Jay was actually interested in not needing Embargo tokens. Then, two of the biggest duds to replace, I couldn't. In the end it got a tweaked rulebook and fixed wordings/layout (including Pirate Ship being clear about Guilds), but no new cards. And nothing else has new cards on the way either.
I did think of "what about an update pack with 1-2 new cards from each of several expansions." That didn't happen though.
The revisions have been a crazy amount of work, not all of it done yet (I could be proofreading a revised rulebook as we speak); I do not imagine I will revisit this concept any time soon.