Why buy used? Check out Yamaha!
The Plinius is the cream of the crop you listed IMHO. I have a friend who owns the 8100 and I previously owned an 8200. They were both recommended by another friend who uses Audio Research tube amps, so you know where the recommendation's coming from.... Really good amps. The Arcam is also probably pretty good. I owned an Arcam Alpha 10 and there's one for sale on A-goN right now for a decent price. It was a good integrated amp and I enjoyed it. But it's not as good as the Plinius.
BTW, my current amp is a Rega Elicit-R Integrated. It's out of your current price range at $1500 +/- $200 used. But it's worth it if you up your budget.
This is just my opinion, so feel free to verify it with a dealer or independent service shop like the folks at www.champlifier.com . The Plinius 8100 is a typical integrated stereo amplifier. The typical service needs would be something like the replacement of old/failed capacitors or power transistors. This is a simple repair for a professional, as long as the parts are available. Caps are no problem. Power transistors probably would not be a problem either. Where you get into serviceability issues is with proprietary electronics like PCA boards, etc. This is more of a problem with HT Receivers and electronic that have computer controlled switching, displays, etc. The Plinius 8100, 8150, 8200 are simple units that don't have all that unnecessary stuff, so you should be safe and serviceable for a long time to come.
I was recently in the same market as you are. I tried the Creek Classic 5350SE, which has a bit more power than the 5250 that tgrisham recommended. I liked it a lot; but eventually settled on a Primare I32; which would be hard to find within your budget. It replaced a Rotel RX1053, which I still have a lot of respect for. Dollar for dollar a better deal than Arcams; I thought.
Bel Canto and Classe were also on my short list, but I think the Primare has made me a Class D convert.