I would say given the costly upgrade fees you'll have to pay just for the privilege of using your miles to upgrade (up to $450 each way depending on fare class), you're better off taking a risk on the revenue upgrade which you can secure 24 hours before the flight as an elite. This will only cost you around $275 each way out of LAX. If you're going in late September, you'll probably be fine. I didn't ever not get a REVUP out of LAX (do a search on revup or uprev if you're not familiar with this),

On the other hand, if not having a confirmed BF seat will give you heartburn - do the upgrade. FWIW, I suspect the return flight is more popular (and hence worth upgrading if you can) since it is overnight. But I would still take the risk..