I agree, if you go for dedicated clients (irc, mail, rss) you will get more power/functionality if you need them; but I feel that in Opera I get the optimal balance between functionality and complexity. To each his own.
Still, I don't understand what benefits are to explicitly disabling Opera's built-in torrent client; why not use something else?
Opera always override default torrent application on my machine. I found it to be easier to just disable Opera's built-in BitTorrent than changing back the default every few days. I wish they have this simple "Use Opera to handle BitTorrent" checkbox in the Preferences.
I think all Opera's extra goodies are good only if you expect 75% of functionalities. E.g. Opera Chat still don't support encoding fallback (X-chat, IRSSI, mIRC, etc. does), or it is not very obvious to disable the built-in BitTorrent client (disable it in `about:config` by yourself), Opera Link that only merge two bookmarks together, requiring me to manually delete all default bookmarks before (or after) syncing, etc.
But it is a really good browser: fast, has minimum resource usage. I wish there is Opera Lite. (And hope Opera team to finally fix Asian language support.)