As a happy man who is married to a gorgeous, willing participant in wet and messy adventures, I have noticed lately a large contradiction in the way we enjoy our WAM.
When watching videos, we enjoy them for the "inspiration" if you will. The substance used or the outfit the woman (or women) wears. We also enjoy watching them covered from head to toe, usually in nice clothes. Our favorites being similar to www.messy-online.com or www.wamhunter.com and those same styles of mess. I prefer a girl in tight jeans and t-shirt, she prefers office wear.
Now, with that said, when it comes to messing up my wife (or getting her wet), we have found that "less is more". We certainly enjoy messing her in her jeans and t-shirt just as much as, say a good thong and tank top. We just also noticed that we use a lot less substance.
It could be that she is quite sensitive to the smells and has EXTREMELY sensitive skin, but it turns us on more to use just enough mess to cover her T&A and then we go shower up
Has anyone else experienced the same "less is more" when getting actually messy, or is it just us?

In my experience this has been true because my SO hated WAM; so yes, less was definitely more.

For me personally I don't really know because I've only had maybe 2 messy experiences in my life and like 5 wetlook ones. I'd like to think more is more, but then cleanup is a bitch. Honestly, I'd just take anything I could get at this point.

I have found that aswell, I have enjoyed a few messy sessions where the lady is dressed in smart office or party wear and have been more aroused seeing the clothes partly messed up then the whole outfit. I have always adored a satin blouse or shirt worn under a trouser or skirt suit and seeing the cream, custard or strawberry sauce over a silver satin blouse around the breast area making the blouse see through in that part and a little custard over the jacket so you know that strict boss look is now messed and unable to be worn to work seems more of a turn on to me then stacks of liquids and gunge over the whole outfit. Cannot explain why just my thing I suppose.

Watching is entirely visual, so generally more is more. But participating is far more tactile, and to an extent, especially if clothed, the first few pours, where the wetness of the mess is wetting and messing clean, dry material, has the biggest impact.

Imagine a woman in a smart trouser suit, worn over silk panties and a satin blouse. If filming a video, we would pour several cans of custard into her trousers fairly quickly, so we could soon see the mess soaking through the trousers from the inside. But in a play situation, just half a can poured into her knickers is plenty to radically change how the outfit feels to wear, she will feel very messy even though nothing will significantly show on the outside of her clothes for some time. If she's actually into WAM and gets off on feeling messy, that half can will probably be more than enough to drive her wild. Cleanup is also easier if less has been used - in this example she could simply shower in her outfit and then take the messy clothes off in the shower, no need for plastic sheeting or drop cloths.

A couple could have a fantastic clothed messy experience together using just one can of custard between them, half each in each other's underwear. But this wouldn't be as much fun to watch as people totally slathering each other in mess is.

Firstly, the question posed in your body text is tangential from the headline question that drew me in. I'm going to answer both.

WAM is, by far, a more visual thing for me than it is a sensual thing. Although I am married to a partner who indulges me, the practical aspects of it all are far less appealing than the idea that pictures and video can be produced of her being messed up. Messy sessions are ephemeral - but videos and pictures provide a permanent document to be enjoyed again and again.

Having said that, we've done both - ie done messy sessions which included sex that were not filmed or photographed. Ironically, it's a fact that neither of us particularly likes being messy.

I prefer videos. Plus - and this is where I really lucked out - my other half is more than willing to not only appear in them, but also get very dressed up before being totally and utterly trashed with goo. I really enjoy the process - which - because we're making a film - is longer and more arduous. So that's why I expressly make videos. They're for me to watch, really. But, because we are in a relationship, they are also mutually enjoyable and intimate in ways they wouldn't be in a professional model/producer dynamic. I can get carried away in ways that would just be totally inappropriate otherwise. A dream come true.

But, yes, the mess you need to make to really get the effect across on video (I've found) is far, far greater than it needs to be for a 'private' intimate session. In private, you can make a lot of mess with a couple of cartons of custard and half a dozen modest pies. To be fair, it would be unreasonable to expect most uninitiated WAMmers' partners to endure much more than that.