We bought 2 32" vanities to replace our one 73" double sink unit only to find that they both have left side sinks. I was going to build a ~10" shelving between the 2 but now my wife says that no matter what we do, it will look silly to have the sinks on the left of both vanities. Any ideas? And no, they cannot be returned.

I would consider losing some income by removing the sinks. Removing counter tops.
Install cabinets where they need to be.
Stitch them together somehow.
Then i would buy a new 1 piece top and install it along with some matching 4 inch backer.
Then i would layout new sink holes where they need to be and cut them with a drilled pilot hole and jigsaw. Install sinks with some silicone , install new plumbing etc.

Sounds like you can either get the sinks balanced or the cabinets, but not both.

How will this work: (without knowing how far left those sinks are)

Starting from the right side - place one vanity, then place the second vanity and finally on the extreme left, add the 10" to 11" filler. Depending on the offset of the sinks, that filler may be enough to even out the sink placement across the 73" width.

Purchase one for the right side and sell the one.