We've taken down quit a few but always cable the top and have something hooked to them just in case, still it takes a lot of time and money to get them down, so if anyone wants to run around and use just a sledge hammer to knock them down, good luck, I'll watch from a safe distance and see how it all works out. There are some we won't take down though, they are way too dangerous for me to work on.
I'm also curious Montee, with the taking them down as you go as they are unloaded how does that work if you don't have a tripod to hold the unloader in place, all the silo's I've ever seen either had ring drive unloaders or surface ground wheel drive unloaders and you still needed the cable to hold them off the silage as you unloaded them, only a jamesway unloader that sat on the silage and had the bullet pulled up the center would work like you described, all others need the cable to support the unloader?
Upright silos of any make are sure a thing of the past, at one time we had 6 we used every day, and now they are either gone or abandoned for good, bunkers have taken the market over completely and for plenty of good reasons. I too have seen the excavator demo's on the net, looks way too dangerous to me, I'd think blowing them with explosives would be a safer way to do it to me.
Last year a guy near me almost got killed trying to knock over a cement stave silo with an excavator, it landed on his cab and crushed the cab, he got out but was in critical condition the last I heard, by the looks of the machine, its a miracle he even survived.