There are a fair few questions in your post so I'll try to answer them one at a time :
Can anyone point me to some WSS dutch uniforms, especially cavalry, artillery and dragoons? Infantry too.
The most comprehensive work currently available on the subject is Robert Hall, Iain Stanford and Yves Roumégoux's
Flags and Uniforms of the Dutch Army 1685-1715, available in print form from the Pike & Shot Society and as a CD-Rom from Baccus in Europe and On Military Matters in the US :
http://www.baccus6mm.com/includes/products/publications/spanishsuccession/spanishsuccession_text.inc.phpThis is the one to get if you are serious about the period. It's not cheap (£48 in CD form and £50 to £75 as a book) but it's the best in terms of in-depth coverage. If you want something less pricey, the old but commendable booklet on William III's Dutch army by Alan Sapherson may still be in print, or available from second-hand dealers. It's obviously not as extensive as Hall's mighty tome and it contains a few errors that have been rectified since its publication but most of it is still good. Try Caliver Books if you want to get hold of it :
http://www.caliverbooks.com/Partizan%20Press/partizan_PP17thC-18thC.shtml Would the uniforms colors have changed much between the nine years war and the WSS?
Many retained the same coat colours and facings but some adopted new uniforms when regiments were taken over by new colonels. Flags also had a tendency to change with new owners (though being very expensive items colours were usually not retired until they literally fell apart and amounted to little more than rags on a pole).
Would tricornes have replaced earlier hats by then? Can I use the same troops for both wars?
The tricorne vs broad-brimmed hat debate is something of an old chestnut. Suffice to say that tricornes supposedly replaced hats over the turn of the 18th century, though one can wonder how long a tricorne retained its shape in the field after a few months spent campaigning in the rain.
As for using the same units for both wars, it's all down to how picky you are. I personally wouldn't but I can understand people wanting to make the most of what they have. If you intend to do so, remember to base your pikemen separately so they can be removed from the unit for its post 1697 incarnation since the venerable pike had all but disappeared from the battlefield by the time the WSS broke out.