Accuphase fans. Newer & Lower vs Older & Higher model?

Hi all

I am not rich, not a techie, no expereiences in Hi-Fi, and have no dealers nearby

So I need your help.

I've been craving for integrated amplifier, either Luxman or Accuphase. I am going to buy a used one off eBay from Japan

Since I am not able to afford current generation of Accuphase, the ultimate final Two is Accuphase E-470 and Luxman 507. Of course, I will go down to previous models if they are not too old.

My wife thinks Accuphase is prettier than Luxman so I will go for Accuphase probably

I am considering following models, around 5K budget

E-470~450, 380~360, 550~530

My question is

Should I buy a Newer generation but Lower model? Or Older generation but Higher model?

For example, 470 vs 380 vs 550? 

And How old is too old? X20?

Regards,

Arron