if it can be welded then weld it, shame to throw away a car, especially a vw, if the rest of it is ok. besides if everyone had that attitude then there would be NO mk1's on the road at all!
jasonpi-restore the bad boy!!!!!! 
yeah, welding is fine. but you wont cure the problem. your just putting your problems off for another day.
striping the car down and replacing a whole section like that is quite simply uneconomical unless the car has some intrinsic value to you, eg, its special cause you had your first shag in it or something.
but if the car is devoid of such sentimentality, bin it. save your money, and find one that hasn't got a rotten arse. there are plenty of VWs still out there that are okay.
again, personally, with all its known problems i'd be asking a very serious question - what don't you know about? strip it to the shell. the story will get much worse before it gets better.
i did bin a D reg golf driver last year. the floorpan needed welding. one side of the car was immaculate, the other side was my grandmothers patched quilt. But the car was quite sound, the engine was okay, everything was okay and worked. But it was rotten. Bin.
Tin