Jesse, if you have some sort of breathable waterproof outerwear (Gore-Tex or something similar), I would advise using the Nikwax instead of the silicone spray.
Silicone, when applied to a nylon jacket, will block the pores of the material, creating a sealed environment which make the breathability of the waterproofing material useless – if vapor can get out of the membrane but not out of the nylon jacket, it can’t get out, period, and stays inside the jacket to make you clammy.
Nikwax and other products are developed for waterproof, breathable garments and are a lot better choice. Be aware that if you’d used and abused the raingear, you may never be able to get that DWR back to a usable state. I’ve got a 15yr old The North Face jacket that I didn’t properly care for the first 6-8 years I had it and regardless how much I’ve tried to treat the fabric, I can’t get it to properly shed water any longer.
I’ve linked to a couple of articles regarding rainwear care below. I believe Cabela’s has similar articles but I knew I could find these quicker. I hope this helps, good luck.
http://www.rei.com/learn/expert-advice/rainwear-dwr.html
http://www.rei.com/learn/expert-advice/washing-goretex-outerwear.html