The past two years I've only been able to get out about 10 times/season. However, my outerwear, particularly my pants tend to get dirty due to walking though muddy/unpaved parking lots. I've already washed my stuff once this season with waterproofing detergent. But, I'm afraid if I wash it too much it'll start to lose its waterproofness (is that a word? ), even though I'd be using the waterproofing detergent again.
I only wash my outerware at the end of each season before putting it away. for dirty pant legs and spot washing, I just get a mild detergent, warm water, and a rag and wipe them off. especially for the bottoms of my pant legs
If you have goretex its actually recommend you wash, and put them in the dryer on medium heat to reactivate the DWR. If you do not wash your gear it becomes less breathable due to dirty clogging etc, and can loose its effectiveness to waterproof.
Goretex says you can wash your stuff 10-15 times before you need to redo DWR. I just wasted my AK Hover jacket and pants and they it came out looking great. Took me a while to get my head around the fact that its actually RECOMMENDED to wash and dry goretex. If I can wash them 10-15 times before they loose the water proofing then im going to do it 2 or maybe 3 times a season keeping in mind ill get 50-75 days done in a season.