the stabilization is very usefull, but on this range it is not at all critical. I think you will benefit more of putting that money in another lens.
I would recommend to buy either tamron nonVC or sigma nonOS, key point being 2.8, take the cheapest of both that you can find - they are both good (in japan the tamron is very very cheap, see kakaku.com)
now you have a very good walk around lens !
then, put some money in another speicalised lens ... don't go for the big zoom, try something with a lot of DOF control, something you will have fun with !
good idea depending on what you like might be a 10-22, a 14 2.8 samyang, a 85 1.8/1.4, a 100 (IS) macro, a 50-135 2.8 tokina, a 135 2.0, a MP-E, a TS-E ... you already have a 50mm 1.8 so you can learn from that !
enjoy, those will give you a lot of fun !