If you still have some RA4 developer, do a test to see how black or what colors are still working. with about 20 year old paper perhaps the yellow dye is less active. I have not used the exact old paper but it probably is still good for chemigrams and photograms. As a hack, i have placed a small RGB led with remote control for the colors over the area where I expose photograms. So I can give it a range of colors. That part you can also do on the color enlarger of course.
Old ra4 paper is virtually always fogged beyond reasonable use.
I've used it in the past for pouring carbon tissue on. That's pretty much the only useful application I've found for it.
There's far too little silver in it for chemigrams etc at least in the conventional sense. You could try something along those lines involving a color developer.
Not really. There's little silver in color paper. At best you'll get very, very faint images. Also, I've left color paper out in normal light and it doesn't produce much color; it tends to go kind of muddy and dull, that's all.
Chemigrams involving color developers would seem like the most sure-fire way towards some striking and worthwhile results.