In my opinion for a casual trail /rec rider having a street legal outfit is the way to go!
I live in southern utah and I can save on average a half hour to an hour by riding my bike to the trail and not loading and unloading. It may not seem possible to save that much time, but trust me when ever i go with other people I am constantly waiting for them to get the truck loaded, get fueled up, unload bikes, get dressed, let the bike warm up. Then when you head home it starts all over again. It so nice to throw on your gear at your house, ride, get home, hose down your bike, take off your gear and shower. It makes it that much easier to get a ride in. And do bike maintenence.
So in a nut shell I think it is a good idea.
Keep in mind though that any kit you add will be more weight on your bike.
A great bike for street and trail is the crf 450x
Comes with head and tail light stock, raps out at about 80, plus plenty of low end for trails and dunes. It is heavier than a cr 250 by at least 40 lbs though.