OK, one more try:
Racketeer
Until your next turn, when another player resolves an Action card, if he has 3 or more cards in play, he gains a Copper.
At the beginning of your next turn: discard any number of cards, then +1 Card per card discarded.
$5 Action - Attack - Duration
I think this version solves some of the problems:
- Much easier to tell at-a-glance if playing your next action will penalize you. So it's not as tedious to resolve.
- Copper junking self-balances the effect of the card, sort of like Mountebank. When you get lots of coppers, you're less likely to hit the three action-card threshold again.
- Hits Durations (including itself) a bit harder, since they count towards cards in play, so it will definitely discourage stuff like Double Tac.
- Copper is pretty innocuous as far as junking goes, so there's lots of ways to deal with it besides just sighing and playing BM. Some form of engine that handles the influx of coppers is probably still best on most boards.