weight affects acceleration but has relatively little effect on top speed ...it only results in increased friction on bearings and wind resistance cos weight adds bulk. so keep the spare tyre.
117km from a bike pushing out 22hp seems low....is it possible speedo is faulty?
getting to your question , I think mods are going to cost you more money than its worth, trade it on on a 650 xr and voila...might be the cheaper alternative too