SW1 is supposed to disable the SD card interface, but really isn't working.
Would it work better to put it on ground, or do I need to do something totally different?
Perhaps consider something like a 74AHCT125, and switching the /OE pins. Low on the /OEs would enable the outputs, high would tristate them.
If your intent is to be able to pull the uSD card while the rest of the circuit is powered, you'll have to switch the 3.3V going to the card as well.
Those are a 5.5v chip. Is there any danger with that considering the SD card circuit is 3.3v?
According to Adafruit's website, you can power it with 3.3V (so you'll only see 3.3V levels on the outputs) and it can handle 5V on its inputs.
Or, even better, something like 74LVC245, which is spec'd to run with Vcc's between 1.65V and 3.6V while still accepting 5V on the inputs.
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I had been looking at a 74HC4316, but not sure whether that would work or not.
It seems like it would work so I could disconnect the lines by switching my DIP switch on/off
You didn't say in what way the switch isn't working. In any case, even with the chip switched off, you still have the D12/MISO line active. So it seems you just need to switch both the chip and the SD card with SW1. Or switch the enable pin of the regulator to ground to shut everything down.
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