Most of the beaches out that way are very hard packed cos the gulf is not very tidal. I have done a few beach dives a bit further down the coast at Al Kohbar and the beach there was very long and wide. Ideal for boarding/buggying. The problem with the inland areas of Kuwait is that most of them are very rocky rather than sandy. I would imagine it would be like boarding on a building site. Also, much of the land is owned by the oil companies, so getting access may be a pain!
As for the temperature, for about 6-8 months of the year its far to hot to be excerting yourself outdoors. I was there last July and it was above 50 degrees! And when its cooler - its also usualy very humid!