Perhaps a question for the interview thread, but... is your feeling about promos because promos are a special thing that people don't consider regular cards from regular sets, or because they are an individual thing outside of a full expansion? Or both?
No.
Expansions just beat promos by every metric.
Expansions are great. They are products we sell, that's good for us. They have 25 or so cards, yeeha. I've got space to fiddle with what % of the time I want you to have +Buy or whatever; I can make the cards play well together. You can just buy whatever expansions you want whenever you want to, in English anyway. They have mechanical themes and flavor themes.
Promos exist because publishers want them, to use promotionally. Players like them because they're more stuff, one more card or whatever. But they're harder to get, more expensive per card for players, just one card, no room to balance for sets-of-10, no ability to have a theme. The rules are on a piece of paper you lose and then the internet. We don't sell them (when you buy them on BGG, you are paying BGG). Conceivably they have promotional value but I don't know how to measure that.
When a promo is a cool card, it's depriving an expansion of a cool card. The expansions need all the cool cards they can get, to be awesome expansions; they do not want to pass up on a single cool card, not even one. When a promo is wacky, that's poor, it's this wacky thing you don't have the rules for. If it's too wacky for a set, really, it's too wacky for a promo. And when a promo is dull, why bother?
Promos are good for the situations where there won't be an expansion; instead of that cool card not existing at all, it gets to be a promo. That's it; otherwise they're bad. I just do them to be friendly to publishers.
It feels like I've said this all before and wait, I have:
http://forum.dominionstrategy.com/index.php?topic=5799.msg466880;topicseen#msg466880What I mean is, would you have a different opinion about a card that was sold as its own expansion, but not called a promo? Would you ever consider releasing cards intended to be sold as stand-alone sets? Something that's not "promo-like", good enough that it could be in an expansion, but hey, maybe there's not enough ideas for new full expansions.
A one-card expansion would be bad in a pile of new ways.
The expansions were going to be 20 cards. You get, or got, deals on particular numbers of cards; 25 was a better choice for Intrigue. So they were all going to be 25. Then HiG wanted smaller expansions. They thought these would be good products. They envisioned 5-card expansions. The lowest I was willing to go was 12, due to the issue of wanting to have some effect on the frequency of villages etc.; hence Alchemy. The size was not really what HiG wanted (too big for a small cheap impulse purchase), and it turned out that players significantly prefer the large expansions, as clearly seen from sales. Hence now Cornucopia and Guilds are one box.