Do you think small expansions are a reasonable design choice sometimes, like when you think an idea can be used for only a bunch of cards? Or would you try to avoid them in the future? I'm not exactly sure how much influence HiG, who apparently pushed for small expansions, had during the development of Guilds. Also, do you think any of the small ones would have become a big set if you hadn't had to deliver them small (and quick, fot Alchemy)?
I picked 20 cards as the default expansion size, with 25 cards for the main set. Jay wanted Intrigue to have more cards due to getting particular price quotes for particular numbers of cards. So it was 25 and then that was the default size.
HiG wanted small expansions. They envisioned a cheap impulse-buy option, something like 5 cards. I didn't want to go that low due to wanting a good mix of effects regardless of which expansions you owned. The smaller the sets, the worse you do there. I agreed to half the usual size. So Alchemy is 13 (counting Potion).
Then it seemed like we would alternate. So Cornucopia is also small.
Later on there was the issue of, Dominion and Intrigue were 500 cards, Seaside and Prosperity were 300 cards but had extra bits. Could a set be 300 cards with no bits and just be cheaper, or what? I made Dark Ages 500 cards with no bits to solve the problem there, and the tentative plan was for Hinterlands to be a standalone and thus 500 cards. Jay went back and forth there but ended with Hinterlands at 300 cards, no bits, slightly cheaper.
Guilds existed just to go between Hinterlands and Dark Ages, but Base Cards came out and delayed it, and one small set in a year didn't seem as nice as one gigantic set in a year, so I switched the order. In the end HiG did not get to put out Guilds due to their ending of doing business with RGG. They had no influence on it other than that small expansions only existed because of them.
With Adventures I had more than enough stuff, and was eating up a bunch of space on the Travellers. I decided to go for 400 cards and Jay okay'd it.
Okay so that is the story of the sizes of the expansions to date.
I think bigger is better. There's the reason already stated, that you want a good mix of villages and +Buys and things no matter what group of expansions someone owns. But also, it turns out people didn't like the small expansions as much as the big ones (and not just because of Alchemy's problems). So there's just no push towards small expansions. I might do one if I felt like there was demand for expansions that I couldn't ignore but I only felt up for making a small one. But uh. If it's just, an idea only goes so far, well, an expansion can have more than one idea.
If I hadn't been asked for small sets, then Alchemy would have been a large set. It's hard to say what the rest of it would look like since it had been cannibalized; possibly somewhat like Cornucopia since that's what I ended up with that at all relates to the remaining unmoved Alchemy cards. A big thing there is, there might have been one or two cards that interacted with potions (e.g. +Potion on something), but I bet there would have been no additional potion-costing cards. When Alchemy was big and hadn't been cannibalized, it had even fewer potion-costing cards.
If small sets hadn't been called for then I wouldn't have made Guilds when I did. The ideas were in the file and so I probably would have turned to them first when making Adventures. I don't know what that set would have looked like; some mix of those things and whatever things those things suggested. There probably would have been a few more cards that produced coin tokens, but probably not much more overpay, maybe one card. Overpay was not trivial to do. A large version of Guilds thus would probably have had another mechanic to go with overpay and coin tokens.