Using a new piece of furniture, the Gong, visitors who find a particularly cool / useful tower could give a whack. This would give the tower owner a small bit of iMG, similar to other street actions.
The really cool part though would be letting folks publish an update in their feed (yes, very much like Twitter or ****ville -- but wait, it's something actually useful!) with a link that would let the visitors friends teleport to the relevant tower. Explory!
(You have to make / buy a gong to allow folks to proclaim your tower)