I was snooping around a Mitre10 shop yesterday and found a product that may well be exactly what I'm after.....
Loads of grip bare-foot / sand-shoes / wetsuit-booties without the harsh sandpaper finish

can be applied either by brush or roller.....
dries in 4~6 hours
wash-up with water
comes in 1, 4, & 10lit cans..... ($42 for a 1lit can but I think I can haggle that back to atleast $30 a can

)
available in 12 "natural colors"..... BUT.....
if you buy the 'base-white' it can easily be tinted to any color you want
Rubberised non-slip Coating TREDGRIPMade in Australia by DOMINION PLASTIC INDUSTRIES
more reading @...
http://www.dominionplas.com.au/tredgrip.htm&
http://www.aicoatings.com.au/tredgrip/specifically the tech data sheet (pdf download) @
http://www.aicoatings.com.au/wp-content/uploads/2012/10/Tredgrip-TDS1.pdfdrop into your local hardware store and grab a info card (much like a paint color chart), it has a "sample" on the inside of the actual product
booklet and website both say its ideal for outside and marine enviroments

anyone ever tried it ???
Kingy
EDIT:
I found some pricing and color chart here....
http://www.internati.com.au/Industr...-Water-Based----Rubberised-Groupings.htm