First, remember to multi-quote, it's against forum rules to double post as this is considered bumping.
Now onto my advice, OP, obviously you could care less about voiding your warranty for a little old SSD and a hard drive but I'll leave you with this. If your screen starts failing or your logic board fails or GPU fries or if the iMac starts overheating you're own your own and your $3000 iMac will be very expensive to repair and Apple won't be sympathetic about it. One other thing, when and if your hard drive fails you'll have to keep shipping your iMac back to OWC for repairs rather than just taking to Apple.
You can say that Apple's prices are inflated but at least the iMac and the upgrade components are fully covered under warranty which is worth the upgrade through Apple rather than losing your warranty getting the upgrade through OWC. So with that, NO, the upgrade you have in mind is NOT worth it.