I've thought about getting a pair of sand spikes but for the amount of time I manage to get out, I just make do with a tripod as it covers rocks, piers and all situations. I have wondered whether a decent pair of sand spikes would be nearly as heavy as a tripod anyway. I did see some useful looking sand spikes some years back that had a foot plate halfway down to make it easier to push the spike well into the sand/shingle, but I'm guessing they were welded steel so definitely not light.
Just found these - they're Aluminium and lightweight, but unfortunately from the USA. $33.00.