Arcade was $14.99 (to download) for 4 new characters, balance tweaks, and a new system where you can follow players, auto-download their replays, and set up your own replay channel. I think that’s pretty reasonable.
Super Street Fighter IV retailed at $39.99 and was a different game than SFIV (which sucked). It offered 8 new chars and many other things, but I wasn’t happy about the price here. I only bought Super because Vega (Claw) got a huge buff and I didn’t get much playtime out of vanilla (I preordered the collector’s edition).
Overall, I feel as though I got my money’s worth out of the series, because I’ve played SSFIV much more than any other title on the PS3. In the future however, I won’t be preordering again, and I will wait for the tiers to be released before I buy. And if Vega is not in the game or sucks, I’ll buy it used, if at all.