I'd say it is not just reference - but hard data to suggest Ferrari holds its value whilst Masers do not. In the 3-4 years since I acquired some GS, their value has continued to decline which - especially given the rarity of the Spyder (44 in RHD) actually has me baffled. But in the 5 or 6 years I have been watching, fezzas have certainly headed north for 360 and earlier models. I was able to buy 360M in 2013 for 35K GBP - and they are much further north than that now, whilst all Masers have continued to decline.My reference to investment is simply that I repeatedly see reference to Maserati values falling, but Ferrari hold value better for not dissimilar running costs. Perhaps inaccurate?
The 456 (whether M or GTA) seem to sell OK here in Aus...and certainly the 550's are asking extreme prices (how does 180K GBP sound!). 575 seem a better value proposition - but they and the 599 seemed overwhelmingly in auto not stick.
At least the data I have seen (I cant say cars have sold but I have observed prices) suggests that most 90 model Fezzas have shot up in price - which is why it seems curious you mentioned both they and the 612 may have further to fall. Perhaps you meant this of the 612 only?
I'm curious as to why you excluded both the 575 and 599 from consideration - and went straight from 550 to 612?
if it is entry price I'd be going 456M, if it was future value I would go 550/575M, but my personal favourite is the 599. Some day...some day.