An NVidia 450 for $120-$130 would be a strong GPU upgrade. It would make a HUGE difference in Lotro and DDO. You would come close to maxxing out DDO and could play Lotro at High-ish (not Very High or Ultra High). Also you would get the new DX11 effects in Lotro, which I find to be very nice.
Overclocking the CPU would help also (should be able to get up to 2.6 I would think).
Maybe a Kingwin 1264 or Coolermaster Hyper 212 plus cpu cooler to allow overclocking.
Increasing the RAM wont help you very much unless you also install Win7 64. If you cant fit all that in I would add RAM as the third priority, not the first.