I have just restored one of these so feel able to comment.
The cat D is an issue re the value, knock 25% off the potential asking price ..no interior pics, condition are the seats unblemished ? how is the roof lining and plastics?...
mirrors , well you can get replacements from a breakers yard for around £50 a side but they will need doing, non working mirrors is an MOT fail, knock another 10% off.
Major issue is no master key...expensive and can render the car undrivable without it if the immobiliser /alarm starts playing up...I am not even sure I would buy it without that.
sunroof, well it could be fixed with either a new motor or it could just be seized due to lack of use, either way give a dealer a blank cheque, it could take hours to find the fault or minutes...the one I fixed recently owes me around 4 hours ...and it was mechanical as well, it just required some disassembly and lots of WD40 to get it to work.
central locking fault is likely the bowden cable inside the door(s) needs looking at. at least an hour a side to fix.
Then there are all the other little jobs that will come up when you start, and they will be multiple because I suspect this car has not been loved, its had the bare minimum required to keep it legal and Alfa's need a bit more than that...it could need aux belts, balance belts a variator, does the aircon work ? any warning lights ?no eveidence of any suspension work which after 15 years I can ssure you it will need...also cat D and flat paintwork sounds like a poor repair job to me...water pump and thermostat will need looking at as well and a camblet kit is just sensible on a car that age with no history...as you can see the costs are mounting up!
its a nice colour,It has teledials and a rear spoiler...engine is low mileage...its Lusso so leather and aircon.
personally having just restored one of these and finding job after little job that needed doing unless I was buying from a known Alfa specialist or a fellow forum member or ethusiast I personally would not pay more than about £300 for it, simply becasue they have a way of costing much more than you think they will..
bottom line its worth more in bits...it's really sad as they just are not commanding good money right now, many will end up being scrapped over the next year or two or until the values rise.
sorry to be the bearer of bad news
that said its only an opinion and maybe someone else will have a more positive slant on it...
as an example
and this one
and this one in a really desirable colour..
here is my thinking..
good ones with the 2.0 TS engine are going for around £1500-2000 really good ones maybe, maybe 4k but it would have to be very low mileage and A1 condition in and out, and even then I don't think a TS will sell for that money as its V6 territory, those prices would be with good recent history, all the belts ,a full recent service,lowish mileage and 12 months MOT with everything working.
The things that you describe as as being wrong will cost more than £1000+ to sort out at a garage, and if an enthusiast buys as a project I can't imagine it will cost less than a few hundred in parts and probably a good few man hours.
the mirrors alone are £100 to fix even if you can find ones in the right colour and the bases are normally corroded and will need spraying.
so buy yours at £950 as suggested above and potentially spend hours and hours, or a good £1000 getting it up to scratch? or just go buy one from a dealer with 12 months ticket and everything working for around £1500.
I know what most would do..