I can only conclude that even though removing the spawns would stop a threat to the airfields from the v-bases, this is not enough for you because you would still feel the need to take the v-bases. Only with the spawns removed you have no basis for "needing" to take the v-bases. So it boils down to you needing to have the v-bases made uncapturable to prevent you from your impluses to take the v-bases.
Incorrect conclusion. If there were no spawn from the vbase to the airfield, the TT vbases could be left alone, they would be isolated from the TT airfields.
If you made the vbase uncapturable, and did not remove the spawn, there would be no point in capturing the airfield, because it could never be held against a back door attack....which would ensue in short order.