welcome sean, you'll know if the cams are going when you have a listen at tickover and hear the fast rattely knock or especially driving with window down passing parked cars or walls take accelerator off and you hear the tick/tick/tick of the followers slapping around. if still unsure take off the oil filler and look in (when engine off/stopped!) shine in torch on that lobe and see what its like, run flat head screwdriver over the top from edge to edge. if any wear they will be groved in the middle you will feel it. they only need to have slight groves on each lob on the 4 cams for car to sound strange. they are on their way out at that stage and quickly progress to farm machinery noise! at this point knock 2k of the asking price and i would not take the car unless you trust whoever can do the job or diy yourself. i suppose having a listen to a few known good 2.5tdis would help ..check you tube for the non tractor sounding ones!!
I have just changed 160 v6 tdi cams and t/belt at an initial cost of 1500. I love the car, it has comfort,power,sounds good again but was it worth the money and hastle I had since? theres a lot of stuff comes off during this job and if its not put back together carefully by someone who a) knows what they are doing, b) cares what they do, you'll run into months of issues trying to trace the faults.
i had oil leaks that took weeks to trace, braking probs due to damaged vacuum pump seal, nipped wire causing starting probs, damaged hose letting in air, dirt in my fuel injectors, maf got something dropped on it while off, and a clogged egr caused by loose cabon in the intake manifold...all cumulating in the car running like a bag of cr@p after spending that amount i was gutted. so i have since spent a further few 100 to rectify these issues 1 by 1 over 5 months (not including my time!) and of course no fault codes shown up to help diagnose! The prob with audis is they are expensive if they go wrong so diy-ing is my only option.
owning a 160 a4 cab i would say that for a bigish lump there is not a lot of room inside. there is plenty of driving/passanger room but stick 2 car seats in the back you'll only have room for your lunchbox between them! recline them and your kids will have their feet all over your leather headrests! plus break the weak centre armrest! but thats the price you pay for comfort, solid built / quiet ride. the boot is large but has no depth so it means pulling the wheels of the 3 wheel buggie and spending 5 mins assembling the fold up/down parts while the kids screem to get out! so that stops the missus driving it anyway
amazingly we fit better into her nissan almera hatchback..work that out and im serious!
suppose may mention fuel economy too...2.5s only about 35-38mpg im afraid dunno wha the scoob was but the 2.5 aint cheap to run or tax . still rather ther 2.5 than the 1.9. especially if towing is needed.
i'd go for the 4wd 180 avant if you can...good history and gearbox services needed too...then you'll have peace of mind , power and room!