[ctrlz]

I went ahead and deleted the sound tube this weekend. The benefits that made the most difference to me were:
1) reduced cabin noise enhances stereo sound, particularly from the front A-pillar and center speakers. This was immediately noticeable to me.
2) There is now a greater difference between the cabin noise for Sport and Touring modes. I have the NPP exhaust. Since there was never a way to turn off the induction noise, it is pretty easy to understand why deleting that would make it easier to hear the differences in the exhaust modes.

I used the Hillman 1" plugs which I found in the boxed fastener area of my hardware store. It is Hillman #54179-C. The caps have a Christmas tree-like configuration and have plenty of lip to prevent being sucked in. I loosened the intake end enough to get the 90 degree fitting off, put the cap there, and re-crimped with some diagonal pliers and screwdrivers. Plenty tight to hold it. On the firewall fitting, the cap was not that snug, so I dabbed a bit of black silicone on the edges to hold it. I'll be able to get it off should I ever want to reinstall the tube.