The way i see it (and i own a mk3 8v)
The 8v is a great town car, and you can have some traffic light fun, and its not slow, but its not fast. But it is a GTI.
Im upgrading my 8v to a VR6 with the sight to supercharge it, almost trippling my bhp.
Im not in search of big bhp because the 8v isnt enough for what i use the car for, but more for the fact i can, and it looks and sounds awesome.
People that hate the 8v mk3, tend to have something slower and non gti

Mine hasnt broken down and needed help threads every 2 days, unlike a lot of other cars on the forum

Worth upgrading to an ABF? Not really.
If the car is worth upgrading, you might as well do a VR, as you need to change all bits to fit a 16v or a VR6.
But again from experience, upgrading a mk3 engine is NOT easy, and i havnt even took the 8v out yet. lol