aztruck,
Interesting question...Few observations that may help you. INS doesnt care how many visas you have in your passport it only cares for which visa you enter the US with. This then better correspond to what you are actually doing...For example...if you enter with your Airline Crew C1/D visa and you are on vacation they that could cause a problem because you are not actually doing what the visa is intendet for.
You can sum up visa requirements with what you intend to do. For example if you are going to school then you need a student visa. If you happen to go on vacation while you are at school your main intend is still to be a student even though you are currently on vacation...have I confused you enough
If you are flying your own airplane and not actually enrolling in a school then a Tourist visa should suffice..but this is where it gets tricky...if you enroll in a school (for a CFI renewal) and fly with an instructor it may not fall under "vacation" and a Tourist Visa would NOT be enough...bottom line a lot is up for interpretation and believe it or not the US embassy employees which actually work for the state department don't always agree with INS which is Dept. of Justice. So I would advise you if you are going to renew your CFI to add another visa to your collection and get a M-1 Student Visa and use that when you enter...of course talk to the officer when you arrive and simply ask him. I noticed that they are getting much friendlier and helpful and if you have a good attitude about it they will too...
Take care!