Looks sweet, if its been in storage since 1990 you would expect it to be near to rust/rot free.
As for the motor, it would depend on if it was properly prepared for its lay up
And the price of 4500€, at TODAYS exchange rate 4,010.33 GBP so not an unreasonable asking price, if I was looking for a 16v I'd expect to pay that for a good one like this, if it is that good.
In my opinion the price is to cheap, for a car with this many KM's. The Morrette headlights and Cibie Oscar's on the front lead me to think this has seen some rally stages or some sprited road driving in its very early years!
Maybe I'm thinking to deeply about it

but I think if you bought this you would have to pay out alot more on getting it up to scratch........BUT then you would have a Bx16v with aboult 6000 miles

.
I dont think its a museum piece, however for a collecter or a serious 16v enthusiast its a good start for a concourse show car.
Jez
Past 16v's: 89 Ph1 Black, 90 Ph2 Grey, 89 Ph2 Black, 91 Ph2 Grey, 91 Ph2 Black.
Now. 94 Datsun Silvia S14 rice rocket, 85 Peugeot 505 Turbo, 77 Ford Capri.