Couple things I would check before you start riding it:
1. the oil. If he has memory issues make sure the oil is up to the proper level. If the bike is low on oil dont drive it. If the bike has not been used in 12 years (2007 came out in 2006) I dont know if he ever changed it, but oil does degrade over the years just from sitting. Unless you can be sure the oil is less than a year old, I would change it and the filter.
2. the gas: I dont know how he kept it fresh as you said, but gas degrades even faster - after just a few months it can start to gunk up the carbs or fuel injectors, so I would drain the tank and put fresh gas in it, then add 4 ounces of SeaFoam (from walmart auto section), which will help clean out any fuel gunk that might be in the tank or injectors.
3. when you drain the gas tank look inside it from the filler cap with a flash light - if it was not kept full all the time, there is a good chance the inside of the gas tank is rusted. If it is tell us - that will be a problem because the rust could get through the fuel filter and into the carbs/injectors of a bike that has not been used.
As far as the value, its still a 12 year old motorcycle even though it was never ridden. Shock, shaft, brake... seals dry out and will leak after several years. If the engine was not run at all there could be rust on the cylinder walls and other internal parts. One would think a bike with no miles on the odo should be just like new, but that is not always the case. Goto one of the websites that gives the price for used motorcycles, and enter yours as 'excellent condition'. Motorcycles depreciate in value quickly, so it might only be valued at $3k to $4k because of its age.
The good news is a Vstar 1300 is an excellent motorcycle. I hope you find a way to repay him, esp if as I seem to be reading he has some issues thinking clearly. Talk to his wife privately and assure her that you do not want to take advantage of his generosity at the risk of taking advantage of his bad fortune.
Last edited by KCW; 07-16-2018 at 06:26 PM.