While I'm on, he does reckon there's something to be said for using the proper "washing machine cleaner" (or soda crystals) if your machine is at the point where it has a constant foul smell or signs of mould and mildew, but typically you can get away without them.
Wife seems to think powder is more likely to clog it up than liquid, this is wrong then?
In terms of the internal stuff, she's wrong, but there can definitely be clogging problems in the dispenser with powder.
These are typically caused by using tablets in there or with powder that has become lumpy due to the way it has been stored (damp getting into it, etc.)
The way to avoid is is to use the tablets in the drum inside of a little mesh bag, or if your machine supports it just putting the powder (but not the fabric softener) inside of the drum as a matter of course. It won't damage your clothes and it'll keep the dispenser nice and clean as well.
Another handy tip: washing at 30 degrees is generally rubbish (and not even much more economical than a 40 in modern machines), unless you're specifically doing it for delicate items.