"Cows making spiritual benefit" sounds like a rationalization. Better to boycott dairy.
To boycott commercial dairy may seem cow-friendly, but it doesn't address humans' need for milk or how to benefit cows trapped in the dairy industry.
One way to benefit cows is to engage their energy in Krishna's service by offering Him their milk. Anyone can do it. Simultaneously, we can support cow protection programs or otherwise take steps toward creating local, agrarian economies; this includes tilling the land with oxen and offering truly ahimsa milk to Krishna.
Krishna is bhava-grahi-janardana; He accepts only the good from anything offered to Him. When the witch Putana masqueraded as a wet nurse, intending to kill Krishna by poisoning her breast, Krishna not only liberated her from her conditioned body and mind (by sucking out her life), but He awarded her a relationship with Him in the spiritual world as one of His mothers.
Considering this and other statements of shastra (scripture) describing Krishna's affection for cows, as well as Srila Prabhupada's teachings on similar topics, it's helpful to remember that Krishna consciousness is the purifying agent in all things. As Srila Prabhupada wrote to one disciple,
"One of the anomalies of this Kali yuga is that our foodstuffs have been grown with so many chemicals, etc. Actually nothing in this Kali-yuga is pure. The soil is polluted, the air, so many things as well as man's motives, but by firmly establishing our Krishna Consciousness Movement all over the world, such unfavorable conditions can be terminated.
That is our program. So for the present we must tolerate such conditions. Actually, these are material considerations only. By offering our foodstuffs to Krishna with love and devotion, Krishna says he will accept and it becomes spiritually purified because he is the supreme pure. So love and devotion to Krishna is the purifying agent and nullifies all the bad effects of this age of Kali yuga."