[Lafclaria]

Once you get the requisite muscles and movements, 2000 isn't particularly difficult as such, it just takes a long time (and gives you blisters if you launch into it without preparation).
When I do suburi, I like to consider and check every single one. This doesn't mean that I stop and have a think between each swing - as you get more experienced you can analyze on the fly. I find that trying to do a number like 2000 isn't that helpful, as after a while you stop thinking about what you're doing and just getting into a rhythm of swinging back and forth, back and forth, which may be good exercise and increase the range of your shoulder joints, but isn't that conducive to making improvements.
I'm not sure you can consciously aim for 'spiritual improvement' or whatever when doing suburi. This kind of thing works the same in kendo as it does in, say, going to high school. Most people at high school have things like partying, study, girls/boys, whatever on their mind, and few have 'growing up' or 'maturing' as a specific goal. Yet when you graduate and look back at yourself as you were before you started, you realise that you've changed quite a lot without even meaning to. Kendo's like that - concentrate on the kendo itself and the 'spiritual' (damn I hate that word!) part will sort itself out for you.