Here are my 2 cents.
1. If OP has to return EWR, why not simply check the baggage (I assume OP has a connecting flight)?
2. Why not NWK-WTC PATH RT instead? I can absolutely guarantee that PATH is the fastest way to WTC, providing PATH is fully operational. And it is also the cheapest option.
3. Taxi works between NWK and EWR. But why not an extra train ticket instead (NWK is the next northbound stop of EWR).