I think some of what you're being told on the Mapping programs is not quite right, like the (probably unintended) implication that Maemo Mapper doesn't provide turn-by-turn directions. (It does, but you have to download the route ahead-of-time -- it can't do it on the fly and it can't correct for detours or wrong turns. OTOH, it has certain advantages over a typical stand-alone GPS. E.g., you can download maps for free for anywhere in the world. If you're a traveler, that's really cool. Or, you can be on the street and superimpose a satellite photo map over your street map. Etc.) So I would say, see this How-To if you really want to know about Maemo Mapper navigation. For other mapping programs, see the Wiki, which might answer other questions you have, too.

I agree that you sound like a Tablet kinda guy. As for new versus old, you can pick up an N800 or N810 cheaply now on eBay and, if you want to jump on the new device when it comes out, you'll probably be able to re-sell the old one without suffering too steep a loss.