A car is never an asset - read the definition of an "asset". I know some russians who have garages full new of never driven luxury ones.... they call it a "car portfolio". But then you have to go for the rare limited ones I think :-)
I drive a S8 V10 and see it just as drivable moneybox... but cool & powerfull, lol.
Asset:
-a useful or valuable thing, person, or quality
-property owned by a person or comany, regarded as having value and available to meet debts, commitments, or legacies
If I were to default on a loan the bank could take my car as collateral. If my net worth were calculated, the value of my car would be included. A vehicle is an asset if you own it and a liability if you loan it.
As for collecting cars.. I would love a full garage of exotic luxury cars! That would be a dream come true :D My boss had that that same S8 but had to downgrade to an A8L as it was too much power for him... V10 vs V8 (he 75 years old). Awesome car regardless of the engine tho congrats!
The 2nd engine is good now - they got a new plasma-coating or so. Yeah I still don`t want to sell it, lol. I even would have no plan what to take today. Maybe some day a RS6 or so ;-)