outdoors, IMO The n900 is a good device. It seems to me that you already have thought about your priorities wrt what you want in a phone and if the n900 matches your criteria I say go for it. Having said that I suggest asking about alternative devices from another more impartial forum too.

I find my n900 very useful and there isn't much I can't do with it if I put in the effort. Often there are missing features where I would have to seek a workaround but I think that is true of any phone. I think the drawback is that there is very little support outside of this community so you kind of get use to feeling left out reading about releases for iOS and Android only. Being a long time Linux user I've sort of got use to that from the PC market anyway, there are always alternatives that I have to seek out and the same is true for maemo.
Now the device itself I think is great but as you already know support isn't great even from Nokia themselves, you will feel like a second rate citizen but that's never stopped me with Linux and I get by just fine.