Why do you feel the planks are too old? Are they falling off themselves? Cedar siding grays and can show signs of decay on the outside while still being able to protect the structure.
As for alternatives - what part of the country do you live in? If in a region that you can get wild fires, forest fires, those two in themselves may be reasons for switching to a different siding.
Is the climate you live in hot & dry, hot & humid? All make a difference. Remember the siding is a rain screen - it isn't a wind barrier. air barrier.
Color is not the issue, they are cracking and coming off onto pieces on their own, so when I try to remove them to install the poli insulation, there is not going to be anything left.
I was also looking into recycled vinyl type siding... but so far I have not found anything
For cedar plank siding, if you want to remove and reuse, use a punch to push the nails through (or if large nail heads, pull them. its slow.), but if the siding is coming off on its own and the cedar siding is old (50+ years?) then it may be time.
For any siding that you put on afterwards, make sure that you look at how to build "the perfect wall", (building sciences corporation -- or greenbuildingadvisor). You want to make sure that moisture can move out of the house and not be trapped in the wall. If you are adding polyiso, you may want to see if you need some kind of water vapor barrier behind it that allows that moisture from the house to move outward and drip out at the bottom, then shim out the siding over the polyiso so water isn't head on the back side of the siding. If you hadn't already looked at "The perfect wall" details now is a good time to do so. I'm not fond of vinyl because I've seen too many sloppy install jobs by contractors. If you're doing it yourself - you can make sure that the little details are followed and you have a nice installation. Vinyl is not a fire proof siding, Sunlight that is reflected off concave objects (light windows on house next door - with the SHG coatings) can cause vinyl siding to melt and deform.
If you are in an area where you need to worry about fire embers - you may want to reconsider the polyiso and go with something like cement fibre board siding with a rock mineral wool insulation between it and the house. Polyiso also doesn't perform as well during the winter time in really cold climates (zones 6 & 7).... and it is possible to to do a multi-type insulation (one layer over next) if you understand the wall, the moisture movement and your climate zones.