I can't comment on the Wahhabi ideology because I am not a scholar and neither am I aware of how different it is from mainstream Islam.
Speaking of Ibn Saud's alliance with the British,yes,that is true.Before the Americans went to Saudi Arabia and discovered oil,the British played a major role in the politics of the country.After oil was discovered,Ibn Saud' fascination for the British diminished a little.That's when the US took over and that alliance continues till today.
According to my Dad,who's been working in Jeddah for over three decades now,the Saudis at the bureaucratic level,picked up corruption from the British.
Coming to the destruction of the historical sites,I sort of agree with them on this part because I've seen forbidden practices with my own eyes.I was in Saudi in August and in Madinah,there was a guy who had a few stones with him and he was doing some weird things with them in front of the Prophet's(PBUH) grave till the guards snatched them from him and sent him away.Another example,if you've been to Jeddah,there's a huge bicycle at a crossroad purely for decorative purposes.People used to think it was Adam's(AS) bike and they used to pray beside it.And there are other numerous instances where people have indulged in all sorts of bizarre practices including kissing the Maqam Ibrahim and making Sajdah to the Prophet's grave.
In the Haramayn,you have people to prevent people from doing this.But,it's not possible to deploy people at every nook and cranny.So,I think it is justified,but I wouldn't have done it if I was the king.Maybe they should've figured out a different way to contain those practices.
Lastly,about the relaxation of rules for the royal family,it's an open secret.Everyone knows of their indulgences,drinking,gambling,women..you name it.Even the Ulema turn a blind eye to this.Even if a scholar opposes the royal family,then life is made hell for him.You just CANNOT raise an opinion even if it right.
And the religious police is really a big headache..a lot of them were ex convicts who memorized the Quran to shorten their jail terms and later joined the force.They just do whatever they want to,that's why they always have a conventional policeman with them,otherwise the public will beat them up.