Well the extra notice about having an attachment never really bothered me, but I can see how it's a bit cluttery. I definitely agree the apport attachments notices stuff gets out of control.
Anyway, here's a patch that implements what is described in the description.
I didn't test this with apport, but the code tries to detect whether 1 or >1 attachment were provided. In the latter case it'll give the notice that "<N> files were attached to the bug report" which I think is most appropriate.