I really enjoyed my time with my 550 (owned it for only a year). It was beautiful (Rossa Barchetta which is a non-metallic deep red - darker than Rossa Corsa which is the traditional Ferrari Red) and saddle interior.
The motor is fabulous - it has power everywhere from idle to the 7,700rpm redline and it sounded great with the Tubi exhaust (and it was a real dry sump with mechanical throttles - no e-gas nonsense). Even the starter motor has an incredible whirring sound when starting the motor - it was emotional to use - lots of passion.
I also loved the gearbox - very positive shifting and the classic gated shifter was fun (LSD worked well and you need it with 420ft-lbs)!
The car is definitely big and heavy - it is not a sportscar, but it is a fast GT where you can comfortably drive it sideways on slow corners - very controllable.
The biggest fault was the steering. I am very particular about steering and the steering in modern Ferraris is no better than in a new BMW M3. The effort is very light with no real feeling for the road or feedback. It was quick ratio and accurate, but dead (this is unfortunately the direction of most modern cars).
The cost of maintenance is much lower than most Ferraris and I was able to do most of the work myself (just an average home mechanic) - this is not possible with newer models. It is really fun to work on your own Ferrari, even if it's just changing the oil or something easy.
I always liked the brakes (4-piston Brembos, as on newer Porsches) - they never became soft for me, even driving hard in the mountains. I changed my own fluid and pads and it's important to bleed out all the air.
I originally wanted a Daytona (and was lucky enough to drive a couple), but the 550 is much more useable and more reliable.
You obviously have a fantastic fleet of sportscars already, so you don't need the ultimate sportscar here - if you would like a beautiful GT car and can appreciate it for its strengths (i.e. for touring long distances, it's great), you won't be disappointed. It is a ton of car for the money (I sold mine for $10k more than I paid).
Make sure a real Ferrari expert looks over the mechanicals and body carefully before buying.
Good luck!
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73 Carrera RS 2.7 Carbon Fiber replica (1,890 lbs). Former: 73 911S, Two 951S's, 996 C2, 993 C2, 98 Ferrari 550 Maranello
the 550 is a far better car 
), why not ? It would be a great addition to your car collection. 
