Forgive but I couldn't understand what your first point was trying to imply; of course not all Saudis are Wahabis...they, by the way, don't like to be called that ! Who said anything to the contrary ? But the State is intrinsically linked to Abdul Wahab's version of Islam and his subsequent students have ensured the continuance of that relationship.
As for the 2nd and the 3rd points : Why should KSA invest in Pakistan ? Koi Allah wasstei ka kaaam hai investing ? They're out to make money for that is what a business is. Having said that between them and UAE...they've undertaken some admirable philanthropic ventures in Pakistan too. My Dad works at a local hospital that was built by the UAE during Bhutto's time, they've offered to fund it fully from thence on wards by Zia refused so they've only been giving occasional grants and stuff. Just recently their ambassador to Pakistan visited the hospital and promised a further grant to help refurbish the hospital completely. The hospital has been receiving grants from KSA royals too.
Additionally we do hear of rumors of our military acquisitions being funded by the Saudis, the petroleum we got in '98 etc.