Installing new lowering springs. Do I need spring isolators?

Depends on the condition of the stockers. Mine were good but that's because I live in a dry climate. Absolutely no rust on cars around here. Some people don't put them in to get a bit more lowering.

I just got ES isolators. I searched for other options (50 bucks is a lot [to me] for isolators) and the Prothanes can be found for about 10 bucks cheaper for a set (F/R).

I wouldnt want to run without isolators - the NVH could be worse (some say it is, some say it isnt). If this is a DD, I'd use them. I'm also not big on metal-on-metal contact in the suspension.

Good luck.

I put the eurethane isolators on with my new springs last year and there's no noise at all. The stock isolators were extremely worn after 120,000+ miles.

I think not having the isolators might lower the car another 1/4 inch, but I'd rather give that up and have them on. The last thing I need is more noise, unless it's motor or exhaust.