If you can get a good deal on a nice set of tools, and you can afford the initial outlay, it makes sense to go for a full set. No matter what, sooner or later you'll need a crank puller, cone wrenches, bb tool, allen keys, etc.

Most people buy tools as they need them and do fine that way. It hurts a little less in the short term, even though you probably wind up paying more in the long term.

Edit: That Park tool set looks good. You will need those screwdrivers to set the derailer limit and B tension screws on your road bike, to adjust canti spring return tension, and a bunch of other little jobs. I have a chain cleaner and it's nice every once in a while for the road bike.