You reap what you sow in my opinion. If you choose to target my refineries and destroy say 3 releasing 9 harvesters that now swamp my remaining refineries, chances are I am going too use them to best effect probably designate 1 extra to 2 remaining refineries and maybe 1 for the new refinery I build but I will then use the others to help fend off any land attack or support my counter attack OR I may just drop them in your base to block up your refineries pads and cause an interruption in your attacks or spice flow. I personally see it a valid tactic and a good use of my equipment, others will no doubt see it as an exploit of the system but to me it's as valid as many other exploits such as taking advantage of the Minotaur herd targeting system or sonic tank wave....