There are many strikingly obvious differences between a car and a GPS device, just as there is between a car and say, a washing machine. Nobody has suggested that Garmin or their agents does not have parts for 660's available, all that Garmin has said is that they (the manufacturer) will not invite the device in to look at or repair themselves anymore.
The 660 was launched in 2009 as a replacement for the 550, launched in 2006. Garmin no longer support the 550; they no longer actively support the 660 it seems. The OP tells us that the 660 is six years old, which would put it in the very first batches issued. Its on-bike charging capabilities have failed after six years, why nobody knows. Are there alternative repair agents available? Apparently, yes. Will they be able to repair the fault? Who knows. Will the repair agent use genuine Garmin parts or generic 'same as' parts? Who knows? Will it work? Who knows.
If the OP fails to persuade Garmin to repair the six year old - long out of warranty - device and / or cannot persuade them to offer him a replacement at say a discount, then he has two short term choices:
1. To offer the device to a repair agent for an opinion and possible repair
2. Seek to repair it himself
This somewhat garbled thread suggests that the device might be entering mass storage mode when powered by the bike:
http://www.horizonsunlimited.com/hubb/navigation-maps-compass-gps/zumo-660-charging-problems-66080 Feck only knows if they are right but give it a go, it's free to try.
As to the scratched screen? Generic replacement screens are available, along with video instructions as to how to make the replacement.
Here's an example, found in under 10 seconds of a search in Google instead of ranting:
<iframe width="560" height="315" src="https://www.youtube.com/embed/bdgm3ix3N_c" frameborder="0" allowfullscreen></iframe>
Give it a go yourself (if you can be arsed) or post the device off to someone who will, parts plus labour.... A bit of an arse, but not too much, hopefully.
PS Nothing in your post #15 indicates whether you have already tried contacting Garmin about your scratched screen already; though it strongly suggests that you haven't been arsed to. Give it a go. Who knows, they might just say yes.