Attic rain / how much more insulation?

o I have attic rain, the insulation company came and advised there was a significant amount of moisture with multiple contributing factors. The bathroom exhaust fans were installed incorrectly; the house was built in 2008 , has only 8 inches of cellulose, areas in the attic have no insulation and or the batts have shifted and the attic entrance weather stripping is bad.

A quote has been shared with me to bump the cellulose up from 8 inches to 16 (r50) or 20 inches (r60), they will fix the vents and is tall proper flashing, and add better seals on the entrances.

Going from a r50 to r60 on a 1320 sq ft attic is about an extra $450 CDN.

I live in a zone C in Canada, we just had temps range from -30 to -40 Celsius for 3 weeks. The summers can get to 30 Celsius for long periods and even higher. Northern Alberta.

Is the r60 worth it?