Proudnail: Insubstantial

Insubstantial sucks! It's the worst crime that you can perpetrate on your players: tedium. As written, the insubstantial property on monsters halves all damage, except for very odd corner cases. What it is supposed to do it represent the ethereal qualities of ghosts and the like; in fact, making them harder to hit. What has ended up happening is that monsters with the insubstantial quality have gotten about half their normal hit points. Which is good on one hand, I'd hate to have to fight encounters with standard HP insubstantial monsters, it'd take forever! On the other hand, it's pretty bad. Insubstantial + Half HP = just one more layer of math for someone to have to deal with. Here's what I propose you replace the description of insubstantial with, and also bump up the creature's hit points to be in line with its typical role and level counterparts:

Insubstantial
All attackers must reroll every attack roll made against this creature and take the lower of the two values, except if the attack has the fire, force, psychic, or radiant keyword.

Bam, there you go. The martial characters and anyone without access to these keywords are going to have a more difficult time actually hitting the creature, but certainly will still be able to defeat them. Arcane and Divine characters will be able to fight insubstantial creatures with no problem. It's entirely possible that this house rule would totally screw up your game. You may have a party full of fighters, warlords and rogues. They may get obliterated by a few paltry wraiths. This is the risk that D&D heroes must take.