Depends on your budget and your penchant for shiny things!
If the rig works for you and you know it's history then just keep it and change the wheels.
I'd imagine you've got a 4" (101.6mm) PCD on your 8" wheels, which is common, ergo easy to match and therefore cheaper to upgrade. Measure it to make sure.
As Downhilldai has correctly stated, you'll need to check your mudguard clearance. You may get away with moving them 'up' to gain some extra space, but in all likelyhood you'll need to change them and relocate / renew the brackets too.
5.00x10 or 145R10 wheels are circa £50 each (you may need a decent ply rating, depending on the weight of your RIB)
el Cheapo plastic 10" mudguards roughly £6 or £7 each
mudguard brackets circa £3 or £4 each, something like that.
So budget around £120 vs another trailer at £....?