Before 9/11 I wasn't in aviation, so my thoughts on flight deck visits back then would have been along the lines of "wouldn't it be great to look out the windows at the front".
But post 9/11 (again before I was in aviation) when the full details of the atrocities became available, and the 'locked door' policy was created I thought that it was a shame, but fully understood and supported the reasons for it.
My views now (as a member of Cabin Crew) are that passengers should stay out of the flight deck, purely because you don't know what someone is going to do in there. If a passenger was to pull a lever or press a button, they could create a serious problem - so my personal opinion is that I would prefer passengers to only visit the flight deck when the aircraft has landed.