Perhaps make a "sweeping tech" that requires Mines 1. What it will do is give copies of the PDCs that have the sweeping ability. So, without it, you have PDC I-V without sweeping. With it, you get PDC I-V with sweeping. Otherwise, the impending uselessness of mines happens a lot earlier in the game, as it will be much cheaper to research.
That, or just use the normal Mines tech as the tech grid, so Point Defense Weapons 1-5 give PDC I-V. Point Defense Weapons 1 + Mines 1 gives PDC I with sweeping. Point Defense Weapons 2 + Mines 2 gives PDC II with sweeping, and so on. This could get complicated though.
It is up to you really, as it is your mod.