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Oh geeze, these are the tough questions. Plated opens up a lot of riding for sure. That's a no brainer unless your doing MX.
You might ride from prov to hartford on a dirtbike once, but I doubt you would do it twice. The dual sport thing is a double edged sword. You could end up with a pig in the woods that sucks on the road.
It all depends on what style dirt riding you end up liking best. For me, that was definitely MX. It's like trackdays in the dirt. I like woods, but haven't been able to justify having 2 dirtbikes...yet.
To get started, keep it street legal and cheap IMO. That way if you don't love it, or find you like MX better, you can change bikes without taking a bath.
The newer bikes are lighter stronger and handle better. You don't NEED those things at all, but they are nice.