Probably easier to sell private in the long run. It's something I've been thinking about recently, what would be the right time to move mine on, are we talking months or years?
Got a 1.8TS Blackline with 34k on it and Alfa service history for £5225 from a dealer back in feb that had had it part-exed against a van, and sat in stock for a few months and simply wanted rid. They showed me the paperwork, made no money on it at all. Thing was it needed w.pump and cam doing, so I factored that in.
Anyway, since then I've replaced the batter, had the pump and cam done, serviced it, variator done (at same time as pump) fitted a double-din pioneer head unit with built in nav, bluetooth etc, fixed a door handle, fixing a non-folding seat, and as of yesterday had a new radiator fitted. I reckon I've easily invested £1500 into it all-told in 6 months but don't expect (fingers crossed) to have to do much more past the seat and a new pair of front tyres.
I would imagine (hope!) the value is above £5225 now, Parkers says £7500 for "Private - Good" which it is, and £5600 for part-ex (i'd look for a bit more on this considering the cam and pump done) although I've added 8k miles to it in 6 months!
It's a difficult thing to judge, whether to "cash in" and trade it against a new Giulli or keep hold of it for a couple of years and get value for the time/effort I've put in. Tbh the 1.8 is a bit lacking, and the ride is still too firm, but otherwise I love it and the way it looks.