I think the consensus is that Duceppe was trying to be funny, but he couldn't pull it off. Whatever his other leadership qualities may be, Duceppe lacks the media persona required (of course that's what people said about Jean Chrétien in the 80s).
The original Bloc Québécois which was elected to Ottawa in 1993 under Lucien Bouchard was a dynamic energetic team, determined to be the watchdog over Quebec's interests pending sovereignty. With the elapse of 10 years, the team's enthusiasm has waned, the talent pool has dried up, as members are seeking to return to provincial politics or leaving politics altogether. There just isn't that much to motivate a man to remain with a party which can never aspire to form a government nor even the official opposition any more.
If the new Conservative Party sees the light of day and can win enough seats one day to put the Liberals in a minority position such that the Bloc hold the balance of power in Parliament, you may see some renewed interest. However, since minority situations are ephemeral, temporary and unstable by nature, it's unlikely that the Bloc will be able to recruit talent on a continual basis.
So it looks like the best they'll be able to get for a leader is the likes of Gilles Duceppe.
