Hi Jax,
Yes, there's a party atmosphere - fireworks in several locations. I think there's a big event at or near World Trade Centre area (think it's called something else now but you head towards Pratunam).
Another big event is in the riverside area. Last year when the WTC one was cancelled for security reasons (bombs) the river area one still went ahead. We weren't actually there but could see the fireworks from our apartment in Sathorn so pretty spectacular.
If you stayed at a hotel on the river, you wouldn't have to travel. Depending on the hotel chosen, you could be right in the thick of things.