Even if BigDecimal is slightly slower than double, I will withdraw my earlier reservations. While looking into a separate issue, I came across the blog about the replacement of double by BigDecimal in Lucee 6.
The change is apparently intentional. It is meant to increase arithmetical precision and to simplify coding. In other words, incurring a local disadvantage (slightly lower speed) in favour of a global advantage (simplicity and greater precision). I think it is a praiseworthy change.