With all due respect Fro, why mess with success? The little bit you may accomplish by switching it up for a series or two, as I think you are suggesting, would be so minimal, especially compared to the preparation time needed to learn all the different techniques. There are enough teams already playing a base 3-4, that teams know how to attack it, how to block it, and the preparation time that would be needed for your defensive players takes away from what you are trying to do with your base defense.
You can accomplish the same concept by just varying the line calls out of the base 4-3.
And if you may have noticed, there were plenty of instances in the past 2 years, where they went to a "sub" package called the "30-nickel", which is 3 down linemen, 3 LBS and 5 DBs.
They have also started to incorporate some 5 man fronts in 3rd and short situations. Where they stay with 3 LBs and lost a DB depending on the Offensive Personal packages they are facing.
My take on staying with the Base 4-3, is simple. Just be as good as you can be with the people you have and if you execute and play mistake free football, it shouldn't matter what formation you are in!