For the 4" superlift, it is required eventually. I only got 4,000 miles out of my stock one. Others can last up to and past 20,000 miles. I always reccommend carrying the tools with you in the glovebox or something to remove the shaft when it does finally go.
The reason for the new shaft is 98+ front driveshafts rear joint gets put in pretty much a bind because of dropping the differential down for the lift kit. The angle is too much for the joint to handle. This overtime will bind and make the truck shake. Or it'll rip a hole in the boot then spew grease everywhere then eventually bind up and shake the truck.
Here's a thread that shows the alternative to spending the $450-550 for the Superlift shaft. Mine ran me $300 and I use all brand new parts...use junkyard parts and it'll be half the Superlift shaft price....about $200.
The 4" Superlift in my opinion is the best suspension lift available for the 98+ Rangers. Well...now it's the only one that's available. lol. Only downside to the kit are the sway bar end links which are poorly designed. The other kit, RCD, has quite a few downsides...but a couple upsides like coil-overs.