Will full length fenders help keep rims cleaner?
 

When things get wet my rims and brake pads pick up a lot of debris resulting in more wear and poor braking. Do fenders help with this? If they do I'm sold...

no they get dirty because they roll on the wet street, which is dirty. Mudguards will keep you cleaner,

and a bit less road spew is directed backwards , sprayed from the front tire..

^+1. I run full mudguards on two of my bikes. They keep the splatter off of the downtube, bottom bracket and front derailleur, but especially the feet (if your front goes far enough down). However, they don't keep schmutz off of the rims and braking surface, which require a wipe down to remove grit.

If anything, fenders put more stuff on the rims. Water and grime gets flung off the tires, is caught by the fenders, and drips back down onto the tire and rims. The rear fender channels lots of water and grime on your chain. Ride next to somebody with fenders in the rain and check it out. You'll see what I mean.

They do keep the bike itself cleaner, but I don't think they do much of anything for the wheels. I've noticed that without fenders I'm cleaning my bike daily, but after adding fenders, I only have to clean it once a week.

The only things they help keep clean are the frame and YOU.