I've had my W650 since 2001. I bought it when I was 23 years old.
They're great in that they don't break down and the only service you need to do is change the oil and check valve lash about once every 15,000 miles.
That said, if you want my opinion as someone that has had one for years and years, it's a Japanese bike. It's a really cool one and it's an oddity. Metal side covers, chrome fenders, center stand, kick starter... It's in a few ways better than a Triumph Bonneville.
That said, a 270 degree Triumph scrambler is a more fun (and powerful) bike to ride. If I was buying a 4500-5000 dollar bike, it'd be a Triumph Scrambler. I paid 4500 dollars for my W650 in 2001 with 1500 miles on the clock. That's about what I could sell it for (easily) today after putting another 15000 miles on it.
I'm still in search of my ultimate vintage bike. I have no idea if I'll ever find anything that truly clicks with what I have going on in my head. I'm working on restoring a Benelli 650 Tornado that I bought in 2011. Maybe it'll tickle my fancy more.
Anyway, I wanted to chime in about the W650 since I've owned mine for more than a decade now. Great bikes. Relible, well worth the money if it's the sort of thing you want. But I think with depreciation, the Bonnevilles are also reliable and fun bikes. I like the 270 degree engines better though. The W650 is where it's at for 360 degree engine. I had a Yamaha XS650 and I prefer the W650.
The XS650s are going up up up in price just like the CB750.
If you like parallel twins, try to find a used Triumph Scrambler. Especially if you like the TW200.