I highly doubt the "repair / hack-a-rama" is going to "fail" in street driving, and you are "better" than having the rotted areas without the slapped on tin to be honest. I would also hold off until you can have a proper repair as well though. However, if you have other issues like missing leaf springs that have broken off, and the shocks have fallen off... I might agree with you about adding the lift. You really only have one area that a new lift even comes in contact with. Most of the time, a total failure in street driving will result in lots of noise and the spring going through the frame rail. With the axle bolted in place, and the front hanger attached, it should stay pretty much in place. (Been there, and have driven cars with the rear springs that have gone THROUGH trunk floors!)
Just make sure it's repaired properly this time around. Oh, and I would love to be a fly on the wall the next time that mechanic talks to the Hack that slapped those patches on for you! (I still stand by the fact that for $200, it was not billed enough to drop the gas tank and repair that kind of damage)
PS, for the poster that mentioned that he did not "have" to remove his gas tank... Remember, gas does not burn.... it's the fumes. That's a heck of a way to put yourself in the burn / trauma unit. That kind of injury is something you NEVER want to EVER go through in your life! The term "debridement" is something you should never learn about first hand. No body ever catches a gas tank on fire on purpose, but you are creating molten metal around a plastic gas tank, just inches away. It's worth the time to remove the tank, but don't forget to plug the fuel lines too!