I've doucmented my thoughts extensively on BF, so I'll have a go here. There is nothing wrong in trading pick 5 provided you don't undersell the pick. Simply put if you can get a player (palyer pick combo) for pick 5 which is better than what you would otherwise get for pick 5 you are better off trading it.
Thorpe or Reid from last years draft would probably have gone top 5 in any other draft year. Would Henderson, McEvoy or Rance? If yes then keep pick 5, but if we are keeping pick 5 b/c it is pick 5 then we're missing the point. The difficulty is of course assessing how good these guys could be.
I accept you points re who we have drafted in the last 5 years with our first pick - but equally our first pick has produced a couple of failures - Walsh, Power and McMahon (good player yes. 1st round pick????). In Thorpe & Reid you have 2 guys who have been in the AFL system for a year so you have a better picture as to where they are at. Similarly with Roughhead etc. The key is not to over pay. There are about 4 or 5 teams who will chase Judd hard, for a variety of reasons and all aside from Carlton need another pick to make the deal happen.
It really is simple.
Do you think the player you are offered in exchange will be better than who you wish to draft?
If yes, trade, if no, don't trade.
I think it's best to keep the pick and drafting a good kid each year. Even if we won the flag this year, I'd say keep pick 17 and get the best kid available. I think clubs that stay in the first round each year and can pick up a good kid will be able to get sustained success. If you're continually topping up your list with at least one good/very good kid each year you'll be laughing.