the sti's pull half the amount of cable needed to operate the v'brakes, so they were very spongey. I went back and added problem solver travel agents (circa £15 x 2 ) and this improved things a bit but its still not as good as a dedicated road bike.
The other alternative would be to change the V-brakes for centre pull cantilevers, which doesn't have to be expensive in itself. I've got Tektro CR720s on my cross bike, and they're at least as good as the callipers on my old road bike (
Ribble are currently selling them for about £12.75 each).
If you do that, you'll need a cable hangar, which is cheap if you can replace a headset spacer with one that incorporates a cable hangar. It's a bit awkward with some headset/stem combinations, though, because there isn't always a lot of room (as I found when I built my bike). The expensive option would be to change the headset for a CX one that incorporates a cable hangar.