Adam-
You are on the right track. weight reduction is the fastest, easiest way to increase yur bike's performance, both it's acceleration ad braking, and also its suspension's ability to do it's job.
First and most obvious advice: ignore the dummies on this board who'll question why you want to do this or that. Like the previous post^. they contribute nothing to the discussion except to make themselves look ignorant.
As for weight reduction, yes, you are correct; the less power a bike has the more important weight reduction becomes and the more noticable the gains. Your 250 is perfect for a weight reduction program.
first, replace the stock header and pipe with an AP full system. Saves alot of weight and really increases the bikes hi-end performance. This is a must.
Second, reduce your rotating mass. Standard theory is that 1 lb of rotating mass = 7 lbs regular weight. best place to start is an aluminum rear sprocket (while you are at it change your gearing to 15/43, so you'll need a 15t front too). Next, if you are ambititous, take your rear rotor to a machine shop and have then drill it out as much as possible. there's easily 3/4 lb of weight to be lost there. With the alum sprocket and drilled rotor you'll notice better acceleration and braking and better turn in and rear suspension compliance.
Third, believe it or not, your tire choice. tire weight is the least appreciated aspect of weight reduction, yet it can be the most critical. It's rotating mass, and it's mass in the most critical area - rim weight - where it's effect is most pronounced. For example, a 120/70/17 bt-014 front tire weighs 3.8 kgs, while the Dunlop 208 front weighs 4.8 kgs. That means that the bt014 is 2.2 lbs lighter than the same size dunlop. Thats 2.2 lbs, at the farthest pint frm the axle, and thus the most pronounced, that the engine has to accelerate from a dead stop, the brakes must stop, and the suspension must keep firmly planted on the pavement. People spend $3500 on carbon fiber wheels to get similar weight savings in rim weight. You can do it for nothing by choosing the right tires.
My 250 came with the Dunlop GT501s. good, sticky tires, but heavy. As soon as i burn them off i'm going to either te bridgestone bt45s or the bt90s. Much lighter tires.