It seems to me to enable overtaking opportunities you need wide straight tracks. This in turn means less skill is required by the driver to 'keep it on the island' during normal running.
Monaco is tight and twisty and needs tremendous skill and concentration to negotiate safely - but you have few overtaking opportunities.
Catch 22 or what.
In theory, therefore, Valencia should be the perfect track - walls close in to the corners to punish any error, but relatively wide and with two or three long straights.
Unfortunately it is the opposite of the perfect track, so...I dunno.
Purely from a selfish point of view I'm really looking forward to Monaco, particularly if there's no overtaking! I might be able to follow the race for a change...