Sandy,
As you are probably aware I have been playing with "custom grips" for a while and at first throught that using harder materials/rubber impregnated cork was the way forward, BUT, I have run into one or two problems.
The biggest issue is the one you have mentioned as being good
, the difference in hardmess. As you have probably found out, sanding a soft material next to a hard one causes issues...but what happens after a bit of time is that a ridge forms were the softer (cork) material compresses and the harder material doesnt. (Probably happens quicker with my 9-11 weights than lighter 2-5 weights though)
If a single accent ring of wood is used where the heel of the hand sits, it can cause a painful blister to appear as the cork either side flex and the harder material doesnt.
BUT, it looks good and I am sure with the litter rods its not such an issue, but one worth remembering, just in case.