There are weak points with high miles, weak fuel pumps, worn oil pumps and blocked pick up pipes. Apart from that I have not really had any issues tuning 1.8T which have gone around the clock. The cams and cranks seem to last forever, I think the most I have see from an agu was 227bhp 245lbft with 211k, only issues after mapping was lean fuel in the torque band due to a old and lazy fuel pump.
I will be tuning my wifes AGU with 165k on the clock with my hybrid turbo to around 280bhp-280lbft using the stock engine as it is now, I also have my mates AGU with 175k which we are going to test a ebay k04-001 to its limits.
IMHO and from working with around on average 4 AGUs alone per week for the last 5 years I would say you have nothing to worry about, as long as the supporting items are up to the job...