yes I'd turn this into an RFE.  I made this request as the bug tracker 
we use internally at work gained the + and - feature for its equivalent 
of a nosy list and there was much rejoicing among all users.

As for supporting -, I'm suggesting that the button change based on the 
users presence in the list or not.  It isn't difficult to support both 
and people do eventually decide they don't want to hear from some bugs.  
but agreed, + is more often used than -.

(granted you could also consider this an RFE to upstream some of the 
changes we've made in the bugs.python.org roundup tree.  less changes 
for us to maintain and others benefit.)