Lots of different opinions out there. You could search and read threads for a week and not even come close to covering all of them. I've had a couple different IFS 4Runners, and my current wheeling rig is an '85 with a factory solid axle. Here's how it breaks down for me:
IFS, in general, is more versatile, more comfortable, and to an extent safer than a solid front axle. It handles better, it soaks up bumps better, it's less likely to fling you in the air and less likely to topple you when cornering at speed. Those benefits come at the expense of sturdiness, the IFS CV axle has to flex and rotate to greater degrees than a solid axle birfield or ujoint, so it's a little bit more likely to break when stressed. The solid axle also has the benefit of being easier to lift and add moderate amounts of flex to. Each has their own characteristic when flexing out - the IFS is more likely to cause the truck to lean away from the obstacle, and too much of that can throw your center of balance off and cause a roll. On the other hand, the IFS keeps you lower than the solid axle when flexing, which can prevent an IFS truck from rolling in the same spot that'll put a solid axle truck on it's roof.
That's just IFS vs SA in general, though. The Toyota CV axle is actually fairly stout, and can handle some decent abuse. It's also very easy to mod it to a long travel setup that flexes just as well as a modded solid axle. I'd bet 9 out of 10 guys who SAS their 4Runners are doing it for macho points and don't actually come anywhere near using the full capability of their IFS. The guy you know who stuck that JGC axle under the front of his 4Runner is exhibit A - I'm sure he's much more impressed with his truck now, but that Dana 30 is actually a weaker axle than the Toyota IFS he removed. If he really uses it at all, he'll be breaking ujoints like they're going out of style, and if he doesn't, he's downgraded the versatility and reliability of his 4Runner for nothing. He's a victim of The Cult Of The Solid Axle.
If you're thinking about swapping, ask yourself when's the last time you broke a CV on the trail, let that be your guide. If you're breaking CV shafts left and right, it's maybe time to think about a swap (or an upgrade to RCVs, if you're flush). Otherwise, the IFS is almost always a better choice in my opinion.
