Aerobars - worth the money?

For that short of a ride, you probably wouldn't notice any worthwhile improvements--especially when you consider the time it takes to put them on (if you don't plan to leave them on all the time), and the way it changes your position. To most effectively use aerobars, and to get the most benefit out of them you would most likely need to tweak your position as well. For a monthly 11mi ride--not worth it in my opinion. This is especially true if you won't use the aerobars for anything else. However, if you want to get better at time trialing for whatever reason, then by all means, its a necessary piece of equipment.

Yeah... I would say that a $70 pair of clip ons would be well worth the money for the type of gains you would notice. My understanding is that aero bars make a bigger difference than deep dish wheels, yet they cost 5% as much as a good pair of aero wheels. Read these two articles and then decide, or save yourself some time and just buy some clip ons - it seems to be a no-brainer:
http://www.biketechreview.com/archive/equip_significant.htm
http://www.biketechreview.com/performance/pareto.htm