I'm no pro at the disc dyeing at all, but I have indeed spray painted several discs to make them more visible. If you do it "the right way", it will NOT hurt the disc at all and will barely add a gram of weight. In fact, it actually made the discs fly a little better (due to the tiny 'bumpy' surface of the spray paint helping to break up wind resistance).
The first rule in "The Right Way" is to pick a disc that is a light enough color to begin with. A dark color will be a waste of your time.
The Second, YOU MUST BE PATIENT WITH THE PAINTING. Doing spray paint right takes time and several small coats.
How: thoroughly clean the surface of the disc and then give it a quick rub down with some steel wool. Put the disc on a safe surface with at least 3 feet of coverage on all sides (so you don't end up painting the ground around it). MOST IMPORTANT OF ALL: spray from about 2 feet away in sweeping passes. Point away from the disc and then push the nozzle just as you start to sweep from right to left across the disc and then let go of the nozzle right as you finish your sweep. Then, point away from the disc and then push the nozzle just as you start to sweep from left to right across the disc and then let go of the nozzle right as you finish that sweep. Start at the the top of the area you're spraying and slowly move down a little more with each pass, remembering to stay 2ft away. You'll build up a rhythm after very little practice.
Your first coat should be so light that you can't really see it unless you look really hard. Each coat should be just a mist of color and then let it dry for 5 minutes or longer between each tiny little coat.
The spray paint should never be thick enough to block out the stamp on the disc.
If you do it carefully, it'll look just like the DX-Eagle from my bag. I picked it up from a garage sale for 50 cents. It was a stupid cream color and was really hard to see in the tall grass or brush, but I liked throwing it. Granted, I sprayed it a long time ago and it has been well used since I did, but this is what it looks like right now.
If you try to spray a dark colored disc, like this purple DX-Stingray, it will barely do anything for you.
I used the RustOleum brand Specialty Florescent Orange spray paint. The Pink of the same brand was also very vivid and easy to see. I have painted DX plastic (because it's practically impossible to dye), Champion plastic (because dyeing wasn't an option at that time) and a Star plastic. They all produced really good results.
Had a friend who tried putting on too much spray paint at once and too much paint in general and got runs and flaking; and his discs were really rigid and about 10 grams heavier. He was able to get it all off with mineral spirits and they're fine now.
P.S. I understand that painting will make a disc ineligible for tournament play. Meh.
