MO
It seems like you don't have the opportunity to ride a dirtbike and you don't own one. That being said i don't see how taking a 1 day dirtbike course is going to help improve your streetbike skills much.
If you were going to continue to ride in the dirt (with a dirtbike) after taking the course i would say sure. They are hopefully good teachers and are capable of explaining, the how/why/when type stuff unlike (your buddy down the road). But just like the road version of the MSF, they are going to put the seeds of particular riding skills in your head, it is then up to you to practice what they preach over the next weeks, months years to become proficient at it.
They will be able to give you those seeds of knowledge but with out a dirtbike to ride every now and then to practice i just don't see it being overly useful. I would not practice dirtbike skills on a streetbike, they are completely different beasts in more ways than i could mention.
I do think some dirt skills can be useful on a streetibke and even the other way around but again what are you going to take home from a crammed 1 day course without a place or bike to practice on?
It looks like you are already comfortable/competent on gravel with your streetbike and do fine. Just remember it's not a dirtbike, it weights 150lbs more and has essentially slick tires so turn it back a notch, keep things smooth.
P.S. if you have loose change and $250 isn't going to be a big deal and you are looking for something to do, then do it
You could always scoot out this way on a weekend, we can ride dirtbikes all day. I can dig up an extra one or two. Cost you less than $250
