Stache, there is nothing silly in your questions & thoughts.
Why are there so many long-term bond funds? I have no idea. Doesn't make a lot of sense to me either. Heck, there is no shortage of weird investment vehicles that make no sense whatsoever, you know. Just a bunch of traps for innocent investing flies...
Adding tax-free muni bonds in your taxable portfolio while a) you are getting in a fairly high tax bracket b) you already filled the tax sheltered part of your portfolio => this is a classic move that many investors in your situation do.
Now as to the high-yield bonds, remember their old nickname? Junk bonds? Ok, this was maybe a tad exaggerated, but fact is those are corporate bonds, and their higher (*average*) return is associated with higher risk. Big companies do go bankrupt (Lehman-Brothers, Nortel or Enron, just to mention a couple). A fairly common view among common sense investors (e.g. the Bogleheads crowd) is that if you want risk, buy equities. But for the more stable & less risky part of your portfolio, you should play it safe, hence avoid corporate (high yield) bonds.
Whether you buy into this view of risk or not, high-yield bonds on a (high bracket) taxable account do not seem to be a very good match. Dividends and taxes will negate all benefits, and all that will be left is risk... Better use munis, then...
Good luck!