I think the most general response that one can give to the question "When should you exchange queens?" is simply "When the position demands it." Strong moves and "best" moves are made based not on the players' preferences, but on the characteristics of the board: pawn structure, piece activity, material imbalances, tactical opportunities, etc.
Perhaps the most obvious indication that the position demands a queen exchange is a tactical shot, as you mentioned in your post. If the exchange of queens will win a pawn or a piece, and it doesn't give the opponent any form of compensation, then it is probably the correct choice.
The other most obvious indication is when one player is ahead in material. Even trades tend to favor the player who is ahead, as this can allow the game to simplify (or "consolidate") to a winning endgame. There are exceptions, of course:
I was considering submiting this as a poll idea, but it involves to questions:
What are you thoughts on creating a queen exchange position? and
What are your thoughts on initiating a a queen exchange?
to explain the first question is where you make your move in such a way that AFTER you move is made your queen is threatened with capture but when and if your openent captures it, you can take theirs.
Either:
your opponents queen is threatening yours, while it (yours) is protected
your both threaten each others queens with other pieces
or the piece threatening you queen in "pinned" against your opponents queen
the second question is when you capure your opponents queen knowing that they can take yours on the next move (which they will probably do in retalition:D)
when I do it (not included here are the times when I'm forced to do it:D)
1) I only do this for tactical purposes, where it just seems to be what call the "strongest move for the position" (if that makes sense LOL)
2) only to avoid or deliver checkmate.
while I'm at it I'll show a position where I created the position complete with the oponents response
btw this board only shows the pieces that were significant to the position (and the posisition of the kings is insignificant aswell)
BTW can one of the staff edit this to get rid of the centred alinmnent it doesn't seem to show up