The disarming speed needs to be decreased and on top of that: Why not make it an "all or nothing" job: Stopping the disarm procedure cancels it entirely, reverting the mine back to 100%.
Walls is a good example for death by running, it takes bloody ages to reach buildings, especially on PP where both doors face the void rather than the base (it makes sense considering all these lame snipers, though). Another good example is the map "Fort" on public games, usually, there are only 1-2 active defenders (if lucky), it still takes ages to check buildings. Combine that with the lovely strategy of putting up defensive mines as an attacker and you won't defuse the C4 in time, even if you acted the second the mine counter decreased.
General speaking, Renegade is and has always been a team-focused game, where the teamwork and coordination should be the goal to achieve victory. Having a single hottie/tech sneaking into your base (*cough* Eyes *cough*) defeats this entirely, as they can bring down crucial infrastructure with the blink of an eye.
Seeing similar discussions while playing, I often hear people stating, that a coordinated team can easily defend against that and it just takes a "skilled" defender to take care of the base. While this may be somewhat true during PUG (where single hottie/tech rampage is still a thing), it's like 98% of the time people will be playing on public without any significant coordination taking place.
Oh and please, do something against these "spawn->crate->humvee->remote-c4" tactic, it is just super cheap and a hit on ref usually means the other team can pretty much surrender from then on. How about having buildings in some sort of reinforced mode in the first 5 minutes that prevents permanent damage (you can still farm money by hitting it's "shield"). Would also prevent flamer/chem rushes on Snow