having experienced both
If you're toting around an M4 you're already in a different world than me. For me as a civilian, life should be experienced differently when shopping at a suburban strip mall on a Sunday than when theoretically patrolling some insurgent haven in Iraq. It's about the quality of one's life, the richness, some of which is not fully realized when one's center is constantly drifting off in rumination over tactics to be used against mythical attackers that never appear.
I might add that experiencing hypervigilance, and living to tell about it, adds a certain richness to life not to be found in more effete pursuits.
Regular, intense, and correct training in self defense actually frees up brain bytes for other pursuits, by moving more and more tactical thought to the level of "background process".
As a civilian, you have a greater range of training available to you than to all but a few very special military members. There's a lot of mall-ninja, make-a-buck tripe out there, but you can also sharpen skills to a level beyond the average battle-tested soldier through quality classes and sports like three-gun and IDPA .
Military training on M-4 and pistol is geared to getting the lowest common denominator up to an acceptable standard. That safety floor, enabling military folks to employ weapons in close proximity without fratting each other, is what folks often point to when they say, "some folks shouldn't carry with a round in the chamber", "only cops should carry handguns" or even, "civilians shouldn't be allowed to have fully automatic weapons." However, civilian folks, with a little initiative, can achieve a level of firearms proficiance far beyond the average military member/cop.
I wouln'd urge a civilian to train like someone carrying and M-4 on MSR Tampa. I'd urge you to train like someone who wants to be able to defend himself with a black rifle, and who wants to be better than the that guy in uniform. After all, you get to train on your terms, because it's fun, not because of what training evolution you're in, or how many rounds are left on teh books for the fiscal year.
Likewise, there are military men who do the minimum training, because they have to as part of their job, and there are those who get the best training they can find--from any source--because they remember what they love about the job....