there is much to be said for the SDM technology. there is also much to be said for sticking with brand name lenses ifyou are spending serious dollars. The brand name lenses are worth something on the second hand market and the brand x's aren't.
While benefits SDM lenses are not available to you unless you have a K100 super,
I wouldn't buy an expensive lens that wasn't SDM at this time, which implies that you should upgrade your camera body first.
P.S. You are missing a awhole world of fun without a macro lens. There is a whole world of things out there the size of your fingernail that go right by you without a macro lens.
For example I had no idea how pretty this violet was until I got a photo of it. You can't even see thte thing unless you lay down on your belly to look at it. Some of natures' prettyist things are pretty small so don't go traipsing through thte tuilips. --- get a macro.