I am personally a big fan of large-scale models of real-life landmarks (contrary to the Architecture line, where some builds use only a few hundred pieces), so I intend on picking it up, but I haven't decided when, or how I will do so.
As an investment, I don't think skyrocketing is the correct word to use when talking of the Tower Bridge. Sets that have skyrocketed and are most well-known were the underdogs - for example, the UCS Imperial Shuttle. Prior to it's retirement, it wasn't a favorite of the majority of investors. I think that sets that are widely talked about as being "great investments" don't grow as much as the conversations on the sets continue, as a general statement, but there are always exceptions.
I'm guessing that this set will double in the first 2 years after retirement, though this number could be WAY off.