It is pretty difficult to load a bike down with all of your touring gear and not have some wobbles in different speed regimes. Here are some ideas to eliminate or limit them:
1) Most really big wobbles are caused by the front wheel being crooked in the drop outs. This is something pretty easy to overlook since unloaded the bike handles fine and that tends to make you think that the problem is elsewhere.
2) Front racks must be centered over the front axle. If you allow your low riders to be rotated to the rear this will offset the weight behind the point of rotation of the front steering and the trail of the bike and the offseting weights will cause a wobble.
3) You can also get a wobble from unequal weights in the front panniers. Always try to equalize the loads from side to side.
Remember that all of this is assuming that the bike doesn't have any wobbles unloaded.
You can pretty much ignore slight wobbles as occur on most touring bikes between certain speeds as long as they never get out of hand and if they disappear as the bike moves through their particular speed.
If you were to build a bicycle that was so stiff that these wobbles didn't occur it would probably be too heavy for normal use. So you are pretty much stuck with at least some hint of wobbles. Strangely enough, some older steel tourers that feel as limp as a noodle often are the most stable bikes.
And of course you can also get wobbles caused because your panniers or rack loads are loose and swinging about.