I'd be very cautious and recommend you weigh your use case before taking anyones advice that any NG Amiga can be a day to day, desktop replacement for a more mainstream machine like a Windows, Linux or Mac box.
I completely agree. However if your usage is fulfilled by the software, hardware and horsepower available then it can be a very enjoyable route to go.
I love my NG systems, but the idea that I could use them to do my day to day business on them is laughable. They are great machines for what they are, but the truth is I couldn't even get my daily work tickets off GDocs on either MOS or my OS4 machine. The browsers puke too much.
I do have occasional problems with GDocs, but I've been more impressed by the availability and stability of MS Web apps (aside from the occasional menu bar malfunction when it first loads).
Honestly, and I know how much people hate the emulation route - it's hard to go wrong with an Amithlon or even dedicated UAE box if you are intent on running older software. I've got both an Amithlon box and a dedicated UAE machine (XP base, boots right into WB 3.1, never even see Windows) and most people would be hard pressed to even recognize they are emulated machines if they were parked in front of them if an old Miggy KB and mouse were there.
I personally don't hate emulation, in fact I enjoy emulation for old games - I just wouldn't want to go back to setting up and maintaining an OS3.9 setup again, even under emulation.
I've got way too comfortable with the things NG (MorphOS in my case) provides out of the box, or with a simple one-click installation with no missing dependencies.
A multi-booting MorphOS/OSX/Linux powerbook/macmini covers all my likely software needs, although I can't remember the last time I booted OSX or Linux - probably some time in January when I was doing my accounts looking for old spreadsheets and invoices.
Having said that, if you enjoy tinkering with the older hardware (and setting up your 'dream amiga' system that you longed for as a teen but could never afford), then keep onto your classic, or upgrade to something more stable (A4KT).
You might also find that you feel like you don't have much left to do with a stable, powerful system that's already got pci, rtg, usb, tcp/ip built-in.
Regarding Amiga always going up in value... so far it has quite steadily increased in value over the last decade or so (unless/until that day when you press the switch and nothing happens.
)