I know my personal preferences with regards to WAM have expanded over the years. It started and still remains primarily with the right texture of mud (after experiencing certain types, I decided they didn't suit my interest enough and my visual response to those faded accordingly) but I quickly gained fantasies of other things (Gak/Oobleck, thick slime like they used to use on Double Dare, etc.)

Visually, a lot has to happen for things other than clay or mud (in the thick form) appeals to me, but that has to do with personal experience. Also, in my case I rarely if ever have had personal experiences with the AMOUNT of WAM that I would find fun to watch visually. I can get turned on with a minimal amount (a few handfuls of pudding, a couple of strategically placed handfuls of creamy peanut butter, etc.) in the experience, but the fantasy will always remain with the extravagant use of things (full pits of mud/clay, bathtubs filled with shaving cream/pudding, the mystery substance by the House of Mess Gals). I do find myself needing it in the visual but with the right story an handful of a substance is plenty.

For me I'd say the answer is both yes and no. I've absolutely noticed that when I started wamming with my wife her simply dipping her fingers in some chocolate sauce was enough to take me over the edge. Then it had to be chocolate on her body, then messy clothes, then other foods, mud, paint and so on. For a while I worried that my messy interests were running their course and I'd soon lose interest altogether. That doesn't seem to have happened, though, over the ten years or so we've been doing such things together and I think the person who mentioned the idea that humans will always seek out novelty has it right. My imagination seems to keep on coming up with new things that excite me, but they're always some form of WAM. It's been great fun, and I think it will go on being so. And while a degree of novelty is part of the fun that doesn't seem to mean I lose interest in WAM any more than in sex itself.