I personally would not use that many miles and cash to upgrade for a flight like that, but the decision is really one that comes down to personal preference.
Think of it this way- what you are REALLY paying for is a more comfortable seat. The food is OK at best and they will give you a few drinks (if you drink). Your $300 could buy you a much better meal and drinks elsewhere.
The 80k miles could potentially be a free trip somewhere for the both of you if you can score a saver ticket.
If the extra comfort is worth the potential loss of a future flight, it makes sense. If you'd rather have the flexibility to use those miles elsewhere, take the E+ option.