We could reduce pressure on the GC by having pre-created instances of many commonly used BsonValues. For example:

BsonBoolean: true, false
BsonDouble, -100.0 to 100.0 in 1.0 increments
BsonInt32/BsonInt64: -100 to 100
BsonString: empty string

The way these would be taken advantage of would be in the implicit conversions from primitive types to BsonValues. For example:

BsonValue a = true; // implicit conversion returns existing BsonBoolean instance for True
BsonValue b = 10.0; // implicit conversion returns existing BsonDouble instance for 10.0
BsonValue c = -1; // implicit conversion returns existing BsonInt32 instance for -1