Hello, everyone. Many thanks for your help and concerns. It's much appreciated.
All told, I dodged a few bullets. The instruments appear to be fine, as I got them out of their cases ASAP wiped them all down, so there's no visible bubbling up in the finishes or wood. The water had reach the lowest portion of the basses, just below the bridges, I think. I've had no time to open every one of their control plates, compartments, etc. up to see if water got into the electronics, however. (That's the unfortunate result of owning too many instruments!). Too much other damage control I've had to deal with. The cases are all opened and airing out in the garage right now, since I had no other location to put them in. (Note to self: get a bigger house!). Today I'm running out to get a new de-humidifier, since it appears my old one got damaged in the flood. I've been running it since day 1 but there's no water in the bucket, so it's turning on but not doing anything. The minute I get a new one, the cases will go back in the basement with it and I'll run it max for a few days. I'm not smelling mildew yet, so hopefully there's still time. The soft cases got it worse, obviously, ans I tried drying them in the dryer, but it didn't work. Unlike the hard cases, they don't open up all the way, so I'm going to have to prop them open somehow when I get them back inside.
I did open up the few pedals and floor board controller that got soaked and sprayed them with compress air. They're airing out now. Amp appears to be alright as well, as the water didn't reach the speaker. The grill looks to be stained with a water line though.
What basically happened was the rubber boot connecting the PVC piping to the sump pump burst open, so I came home to the sump pump shooting water into the air like a geyser. We've been blasted with severe rain these few days and the pressure was too great. I managed to stabilize it/tighten it, and amazingly the sump pump drained out not only any water in the well but in the entire basement as well. (There's a french drain surrounding the pump as well). One little pump draining a 25' x 20' room submerged in 4-6" of water. With the exception of a few little areas with small puddles, the basement dried out completely. Amazing.
The biggest damage came to any paper materials I had on the floor - books, CDs/DVDs, posters, etc. I've been going through that stuff now to see what's salvageable. Wish me luck. This probably was an accident waiting to happen, though I've nver had a flood down there in 8 years of owning the house. All of this obviously will get me rethinking how and where I plan on storing my stuff down the line, as this was my greatest fear in keeping them down there. I thought about the palette idea too, but I'm wondering what I can use other than wood to raise them up. Maybe one of those drummer risers they make out of metal?
I did an incredibly dumb thing when this happened
, and this is why I dodged a few bullets. When I came home and saw/heard the water, I instinctively panicked and ran down into the water to get my basses, later realizing that I had various power strips submerged under the water. Smoke was spewing from one of the power strip's outlets and the cable was melting. Puts things into perspective. As much as this was a disaster for me, in hindsight it could have been much worse and I might not be here right now. No possession is as valuable as my life, so in that respect I was lucky.
Thanks everyone. If you have any more suggestions regarding the preservation of my stuff, I'm all ears.
I was afraid to lay them down so I kept them standing upright, since I wanted to keep the moisture concentrated in the lowest area and was afraid to have it drip further up the cases. In hindsight, I probably should have laid them down. Overall, a few seem fine, some do have a hard cruddy feel to them now, and some are amazingly still damp even after over a week of outdoor drying and dehumidifying. Oddly enough, the ones still wet are all older Fender cases. 
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