It is ok to use spray cleaner on the maf - we all do it! You are right about getting oil on it, any kind of coating (dirt) is bad for it. And you are right to use the denso filters and plugs from the dealer.

Like BamZipPow says think about your o2 sensor. Look at the front one (before the cat) to see if it's as old as everything around it. If it is, get a new one. If you are running rich due to old o2 sensor then you are hurting the cat and that is MONEY there.

Pull one of the vacuum hoses off the intake manifold and the idle should go funky. If it doesn't you have a vacuum leak.